Battery / Power Upgrade 2000 Itasca Suncruiser

[VelocityDave]

So, my situation is similar but different. My motivation is to upgrade power to accommodate a residential refrigerator to replace our failed Norcold. My engineering background is really getting in the way...

What I'm trying to work up is to (a) increase the current "house" battery capacity from it's current 150 AH, two 12V lead acid batteries, to more like 350 AHs of total capacity, as a first step, with allowance for increased solar capacity down the line.

My concerns are these:

1) The coach currently has a 45 amp factory installed "converter" under the kitchen sink. This converter is just a 13.6V output, 120VAC input power supply that keeps the house batteries charged while we're plugged into shore power. The gotcha I'm worried about is this: Simply adding more batteries in parallel to the house batteries to increase the total available AH could likely draw more than 45 amps during initial charging if the battery bank capacity is much depleted. Think about it like this: the batteries will draw all the current they can - there is no current limiter - during charging. If the battery bank is low, it could draw far more than the 45 amp charger could supply, popping the breaker and/or damaging the converter/charger/power supply. Those that have plugged a 10 amp charger onto their dead car battery and observed the charge meter initially being pegged for awhile will understand this issue.

2) Add those extra batteries - where? I think I may have an idea (over the propane tank above the wheel well), but ... ummm ... that may not be too bright given that batteries can occasionally (but very seldomly) explode, catch fire, etc, and having them do that near the propane tank ... well ... I think you can see the concern. Other potential spaces use ship volume that I'd like to retain for storage.

3) Battery Balancing: Again, the washed up engineer in me worries about this. The issue, in short form, is that the long wires between the factory batteries and the additional batteries have some resistance, which causes a (slight) voltage drop, which means that the additional batteries will not either operate or charge to the same voltage as the house batteries. The consequences of that can range from minor to really debilitating.

So, as I engineer this increase in capacity ... Does anyone have any experience doing anything like this? ... THANKS!
Dave

[Marine359]

OK, you bit off a lot Dave.
First, please post details about your rig. Make/model etc. it would also be helpful to know what model Norcold you have. Is it over/under, or side by side absorption, two way, three way? Are you a full-timer?
Then, settle on a budget.
If you’re an engineer, you’ll want your new gear to do exactly what you want. No more, no less. As another engineer, I collected all the data and info, and alternatives, settled on a budget; then designed a solution after choosing the components.
Big issue is what is the space (dimensions) currently occupied by your Norcold. I think we’d all want to know why you’ve settled (or maybe not) on a residential ac powered fridge if maybe a 12v compressor fridge will do. The Dometic 10cf is plenty big for most couples. Those who choose residential are usually full-timers.
If you have the budget and are concerned about mounting space, or keeping your batteries warm, you’ll want to consider LiFePo4, which can deliver much higher amp hours in a much smaller footprint. Any battery upgrade you undertake, whether it is LFP or FLA will benefit from a charging component with higher amperage output. Going to the max rated for your battery will shorten your charge times and max the life of the battery. You can get a high output charger, a hybrid inverter/charger, or use two lesser chargers parallel to get to your target amperage.

My switch to LiFePo4 and hybrid inverter/charger has paid huge dividends. I can now fully charge my batteries in less than two hours from an ac source (SP or generator). That gives me plenty of juice to feed my 12v compressor fridge for days. Keep in mind, if you choose residential fridge, your daily amp/hr fridge consumption will likely be twice as much as 12v, partly because you have to run the inverter constantly. Sticking with 12v will make your life much simpler, straightforward, and less expensive.

Let us know your setup, as there are likely to be members who have your rig and have made mods that work for them. Posting pictures helps.

[VelocityDave]

Jim, thanks for the quick reply!

As I mentioned in the title of my prior post, we're talking about a 2000 Itasca Suncruiser. For those not familiar (and why would you be?) - that's a 38' Class A. The fridge was a Norcold n842im, that lost it's ammonia. The new residential style fridge is already on order.

Some background on me; I'm a retired electrical engineer & engineering manager who builds and races high performance airplanes as a hobby. I'm very much a DIYer, and not afraid of a big project. The last airplane I built took 7 years.

I've looked at LiFePo4 batteries (in fact I've got one in my current airplane). They are great; as you say, they are physically smaller and have higher energy density. But, they aren't really cost efficient enough at this time if you can make more traditional chemistries (and the traditional weight) work (IMHO). In this case, I've decided I'll go with traditional AGM batteries for now.

The specific questions I asked come after much thought. I'm really wondering if there's anyone on this forum that's simply expanded the factory house battery capacity by adding additional batteries. If so, did they have charging issues? Where did they put them? Was battery balance an issue? Any other things pop up as problems that I haven't thought of?

So my question is really pointed at anyone who expanded capacity via adding more batteries. Again, thanks for the quick reply. Is there anyone out there who's done that?

Thanks!
Dave

[creativepart]

You haven't given us full details - but the best I can discern is that you plan to add new FLA batteries in parallel with your existing FLA batteries. If so, that's a fail point right there. Because your existing batteries are "used" they have naturally degraded during this prior use. When you add the new batteries your current batteries will automatically degrade the new batteries down to their level of performance.

To increase the size of your battery bank you'll need to sell off your old batteries and buy a completely new set to begin their new life on your RV. Otherwise your new batteries will be just as old and used as your current batteries. With LiPo4 batteries this is less of an issue. But there is even a limit to new/old battery mixing with LiPo4 batteries.

About your question about charging - the converter will not run wild and pop breakers (not exactly what you said, but you get the point). It will simply output what it can into the bigger battery bank and, no doubt, take twice as long to charge the batteries.

When depleted the internal resistance in the cells of the battery is lower - so yes, it CAN take more amps. But it can only take what it's given it cannot trick your converter to add more amps that it's capable of delivering. Of course, as the batteries eventually charge the internal resistance in the cells increases and your converter - if it's smart enough - will reduce it's output. Question is, is your 22 year old converter a 3-stage smart converter?

Along with changing out the fridge - I suggest you change out the complete battery bank AND the charger portion of your converter/charger. This is probably NOT what you want to hear.

Just an FYI, I moved your posts and responses from that other thread that was really on a different subject into it's very own thread. When your question/thread is not exactly related it should almost always go into a new thread and not be tacked onto someone else's thread.

Hope this helps.

[lenore]

Actually for the Long term cost the LIPO batteries are cheaper per AH. You have to remember that the lithium will last easily 10 years, the AGM will not have that service. Also with a smaller AH lithium you outperform lead acid as they can drain down to 10% easily. Mixing batteries would probably require two different converters to properly charge each chemistry. Totally agree with creativepart on mixing old and new batteries. I dont know how many AH batteries you have, but the wise move is go lithium. There are lots of brands and prices have fallen.

[creativepart]

Originally Posted by VelocityDave

3) Battery Balancing: Again, the washed up engineer in me worries about this. The issue, in short form, is that the long wires between the factory batteries and the additional batteries have some resistance, which causes a (slight) voltage drop, which means that the additional batteries will not either operate or charge to the same voltage as the house batteries. The consequences of that can range from minor to really debilitating.

Absolutely, this will be a significant issue. Best way to proceed is to move the existing batteries to as physically close to the new batteries as possible - read: move them so that they are together physically. Another approach would be to duplicate the length and sizing of the cabling in both sets so that both sets of batteries have the same amount of loss. But even then you need to carefully connect the loads and charging to balance power in and out of the two sets - another reason they should be physically combined into one bank.

[creativepart]

To help set your expectations - I have a residential fridge and 400-amp hours of AGM batteries and a 2000w inverter to run it. Being careful to not deplete my battery bank below ~50% state of charge (SOC) I can run the fridge overnight in my RV about 12 hours. I tested this in my driveway and dry camping for up to 3 days.

I also have 300w of solar and during the day I can get more hours if the sun is unobstructed. More like 14 - 16 hours during the daylight hours.

When dry camping we simply run the generator an hour or so in the morning during breakfast prep and then another hour and a half to two hours in the evening for dinner prep and TV watching, etc. This generally keeps me topped up. I usually try to go to bed at night with the battery bank 95% SOC or higher and wake with a SOC of right around 60%. A lot depends on furnace use during the night as that fan uses a lot of power.

Along with that, a shunt-based battery monitor that reports SOC in percentages and is not voltage based is EXTREMELY helpful/vital.

[VelocityDave]

Thank you CreativePart - it does help! Everything helps! And thanks for moving me to a new thread.

As you mentioned, the ideal solution is to keep the lines going between the batteries as equal as possible (in gauge and length). That's a good reason to have the batteries physically together. There may be other solutions, or partial solutions to this too - such as increasing the gauge of the wire from the remote batteries to the factory batteries to try and shoot for an equivalent resistance to the two parallel connected factory batteries.

In the end, because these batteries are to be connected in parallel, not in series, a battery balancing device won't help.

Regarding your thoughts about old & new batteries in the same "pack", I can see how that'd make a huge difference if the batteries were in series. Can you provide any insight to a real dummy about how that impacts batteries in parallel (assuming no defective cells)?

To me, because I can try to mitigate the "different resistance between the packs" issue, the gotcha that I worry about most is the capacity of the charger. Any thoughts on that?

Anyone else with experience care to chip in to help the new town idiot?

:-)

Dave

[VelocityDave]

And also thanks to Lenore. I guess I hadn't thought much about cost over lifetime... my coach is already 22 years old, and while it's in really good shape, 10 years would be a long time for this old baby.

Dave

[creativepart]

Originally Posted by VelocityDave

Regarding your thoughts about old & new batteries in the same "pack", I can see how that'd make a huge difference if the batteries were in series. Can you provide any insight to a real dummy about how that impacts batteries in parallel (assuming no defective cells)?

Do a google search you'll find dozens of articles some scientific on adding new batteries to an old battery bank.

Here's just one answer I found:

The problem is that a "perfectly good battery" is not the same as one that still has 100% of its capacity as the new one would. As a battery ages it inevitably loses capacity. The deeper it is discharged, the more cycles it is run through, and the time that passes all take their toll. The trouble is there is no practical way to determine how much the capacity has diminished.

Why it is bad to put an old and new battery together is the same as why it is bad to put two batteries of different capacity together (because that's what you've got): the charge will be wrong for one, the other, or most likely both. Too little for the higher battery, too much for the lower one. The greater this difference is the greater the risk of either frying the old battery (in a possible sudden failure) or cutting years off the life of the new one.

Another I found uses equations of resistance to show the internal resistance of the new battery is different than the resistance is of the old battery and your new battery will attempt to charge your old batteries. This response said this can lead to shorts and actually destroy your new batteries.

One solution suggested, which sounded like a bad solution, was to put a battery switch in your RV. Then switch to the old batteries first and when they get low switch to the new batteries.

[VelocityDave]

Originally Posted by creativepart

To help set your expectations - I have a residential fridge and 400-amp hours of AGM batteries and a 2000w inverter to run it. Being careful to not deplete my battery bank below ~50% state of charge (SOC) I can run the fridge overnight in my RV about 12 hours. I tested this in my driveway and dry camping for up to 3 days.

I also have 300w of solar and during the day I can get more hours if the sun is unobstructed. More like 14 - 16 hours during the daylight hours.

When dry camping we simply run the generator an hour or so in the morning during breakfast prep and then another hour and a half to two hours in the evening for dinner prep and TV watching, etc. This generally keeps me topped up. I usually try to go to bed at night with the battery bank 95% SOC or higher and wake with a SOC of right around 60%. A lot depends on furnace use during the night as that fan uses a lot of power.

Along with that, a shunt-based battery monitor that reports SOC in percentages and is not voltage based is EXTREMELY helpful/vital.

That's really helpful information.

And sorry I missed the part in your prior post regarding the charger only putting out whatever it's max charge rate is. My concern with that is twofold; first, running it at max capacity means it'll have a shorter life because it's running hotter (and electronics, in general, don't like to be hot), and secondly, in their wisdom, Itasca (Winnebago) has a 40 amp circuit breaker in line with the 45 amp converter... so if the converter really does try to run at it's maximum load, it'll likely pop that breaker and ruin my day.

And thanks for the pointers rgarding battery banks and mixing old/new batteries. I'll do some looking.

I really do appreciate all of your (and everyone's) insight! I'll keep you informed as I learn the hard way!
Dave

[creativepart]

One thing I forgot to mention in my "expectations" post -- my inverter charger outputs 80 amps when my batteries are low. So, my recharge times should be doubled with your converter/charger. The KOA we're staying at in Tucson for the month is adding some new sites (and Level 2 car chargers) so they turned off all power in the park for 3 hours while electrical work was being done. We didn't even notice because the inverter was on for the first hour or so. When my wife tried to do a load of laundry the load center had shed the washer and the dryer so she couldn't get started.

When the power came back on - we had a table lamp on a non-inverted receptacle that signaled when power was back - my inverter/charger put out 80 amps and my solar added another 8+ amps so the batteries hit 100% pretty quickly. I neglected to check SOC when the power turned back on.

What inverter are you planning on using - your 22 year old inverter or are you updating that as well? If your RV had an inverter to start with it's likely a small wattage Dimensions MSW inverter.

[VelocityDave]

Here's the rest of the story for those that have been trying to help...

I'm replacing my Norcold n842im propane/115v fridge with a Whirlpool WRT115SFDB residential fridge. They are close (but not exactly) the same size. I can make it fit in the space with a few minor adjustments. It will stick out about 1.5 inches farther than the old model. As mentioned, the 22 year old Norcold leaked it's ammonia and is dead. The approximate replacement cost to buy another Norcold is around $2,000, and that sets my budget.

My existing setup, in my 2000 Itasca Suncruiser boasts two 12V 75AH deep cell lead acid batteries for the 12V ship system. That's recharged by a 45A "converter", buried under the kitchen sink. The resulting capacity, assuming perfect batteries, is therefore 150AH.

The new fridge specifies 345 KWH/YR energy rating. That converts to about 945 watts/day. Since a fridge typically runs about 8 hours in a day, that converts to about 118 watts/hour at 120V, or just shy of 10 amps @ 12V while it's running. This is all, of course, assuming no losses.

The batteries I've got are (for longevity) limited to no more than 50% SOC, so in reality I've got only 75 AH to play with before damaging the battery. Again, not considering any losses, that would come close to being enough (75AH/10A = 7.5 hours, and I need about 8 hours / day).

My RV does have a very small solar cell on the roof. I'm not counting on this for anything at this point. It's ripe for replacement with something much bigger!

Now, let's look at this in a real world format...

The pure sine wave inverter I'm looking at (AIMS Power PICOGLF12W12V120AL) claims a nominal efficiency of 88%. Let's assume there's a bit of advertising going on and call that 75%. That means my draw will be more like 13 amps, and my 75AH capacity is then just 5.7 hours or so. Another 75 AH of battery capacity would yield about 8.5 hours or so of capacity ... just enough ... assuming no other loads at all on my 12V house system.

Anyone see anything wrong with this analysis?

If I run a generator for a few hours a day, or if I increase my solar capacity, it'd be pretty close to doable, if I'm right...

Thanks again, everyone. I do really appreciate your thoughts and any real world experiences. I do rough camp for about 2 weeks a year (at the Experimental Aircraft Association Airventure Airshow - which I highly recommend)!
Dave

[creativepart]

The analysis looks OK, but real world may be pretty different. We can't help you much with that. Cool weather you need to allow for the furnace. Hot weather you need to allow for not only fans but for the fridge to work harder and longer.

If I were you, I'd count my savings buying a residential fridge. "Look how much I saved!" But then as a separate budget item I'd spend what it took to sensibly UPDATE and UPGRADE my RV. I'm talking about loosening the budget for the batteries and charger here - and solar.

If your 2000 model year RV has a solar panel it's likely a 10 or 15 watt trickle charger that is not upgradable and is basically worthless. I wouldn't even think of it as "solar powered."

Sometimes, nickle and dimeing to meet an unrealistic budget can be the most expensive "saving" you'll ever do.

[BobC]

There are some good, relatively inexpensive LiFePO4 batteries on the market. I don't know if you've ever watched Will Prowse's videos but he reviews and tests LiFePO4 batteries with teardowns. He also publishes a list batteries he recommends . Keep in mind that LiFePO4 batteries can handle a much larger DOC, theoretically 100% but practically a bit less without damage and maintain a constant voltage throughout. This also reduces the comparative costs between them and traditional batteries.

Batteries - https://www.mobile-solarpower.com/li...batteries.html

Will's YouTube Channel - https://www.youtube.com/channel/UCoj...q8kmJme-5dnN0Q

It may have already been mentioned but LiFePO4 batteries can be mounted anywhere, including inside, in any orientation. You didn't say how much solar you have but adding more is probably definitely in order.

A major factor in all this is your tolerance (and your neighbors) tolerance for running your generator. Personally I'm of the "as little as possible" opinion but others are perfectly comfortable running their generators four to five hours a day. I just don't want to be next to them in a campground.

I've been a LiFePO4 battery watcher with "wait and see" attitude for several years but I think their time has come. Personally, however, I'll stick with my four 6v golf cart batteries for as long as possible. For the most part, my MH has been sitting in storage for the better part of two years due to COVID and unrelated personal health issues. I also don't have a residential fridge and have 320 watts of solar ready to be installed. We previously got by with 100W and then 200W on two successive TTs and a conservative in our power use after years of sailboating.

[VelocityDave]

I always hate it when I see someone post a good question and then just disappear (not that mine was a good question!). Anyway, here's where I'm at and what I've learned.

I went ahead and replaced my Norcold N842IM fridge with the Whirlpool WRT115SFDB residential fridge. I'm using a AIMS Power PICOGLF12W12V120AL inverter to power it.

I had to make some cuts in the Itasca wood paneling to fit the new fridge. It took about a 1/2 inch cut on both sides. I removed and modified a plate on the bottom door hinge so that it didn't stick down quite as far, and I built a "rumble strip" across the bottom front of the fridge to prevent it from moving forward. I then got on the roof and working through the vent hole in the top (there for the old fridge), I fastened a strap, similar to the strap that held in the old fridge, to hold in the new. I then attached that strap to the top rear surface of the fridge via sheet metal screws (and yes, I drilled holes in my brand new fridge!).

The physical installation was then done; and it looks good. My wife even approves, and she's picky!

The electrical installation began with finding a place to mount the large AIMS Power inverter. I chose to remove the outside stereo (which we've never used even once), and put it there. There is ample space there once the stereo faceplate is removed, and the ventilation should be very adequate.

I chose this inverter because it's a "full package" inverter. It includes an AC switch that automatically switches between inverter mode and shore power when the shore power is connected. And, when the shore power is connected, it also switches from an inverter into a battery charger; so when shore power is plugged in, the house batteries are charged (at 70 amps!).

This inverter, coming in at 2500 Watts, is bigtime overkill. I've measured the actual fridge current draw at around 10-12 amps DC, or about 120-140 Watts (at 12.5 VDC)

The connection between the inverter and the house batteries therefore has to be high current capable. It can charge at 70 amps; but the 2500W converter can draw over 200 amps at full capacity (remember, Power = Volts x Amps, or Amps = Power/Volts ... so 2500W at 12.5V DC is 200 Amps, and you have to increase that load to accommodate the inverter losses).

To handle the current, then, you need very large gauge wire, and very short runs. I decided to go with #2 wire; not as big as it should be, but the runs are very short, and the inverter only powers the fridge. Since flexible #2 wire turned out to be hard to find, I bought a 2 gauge jumper cable and used the wire from that.

The inverter charger positive output only had to go about 2 feet, to the junction where the Itasca charger is connected (and I disconnected the old Itasca charger from it's AC input and DC output). Likewise, the inverter charge negative output had a very short run to the Itasca's frame.

I added a 20 Amp breaker into the AC panel for the inverter AC power, and ran a 12 gauge line to the inverter from the breaker.

Now... I had calculated that the fridge would draw about 120-130 Watts when running. This translates to about 10-11 Amps at 12 VDC. With no other loads and perfect batteries (neither of which is true), that would give me well over 10 hours of run time on my (theoretical) 150 AH house battery capacity. But, on a travel day (when I'm not running the generator or plugged into shore power), that likely isn't enough - especially since the batteries can't be counted on to produce 150 AH, and there are certainly other loads. So... here's what I did...

I added a switch (a good quality marine battery selector switch), to gang the house batteries to the truck starter battery...

This took some deliberation. The risk is, if the engine is running (and the alternator is charging the starter battery), AND I plug into shore power, AND the switch is connecting the two battery systems, then the truck alternator will "fight" the charger until one wins, and the other dies.

If however, I'm clever enough to always remember to turn the switch connecting the two battery systems together off when I'm plugging into shore power, then this isn't an issue.

However, if the truck engine is running, and I'm not on shore power, and I throw the switch to connect the two systems, then the house batteries get charged by the truck alternator (and thereby power the fridge). The two battery systems are installed directly next to each other, so the run for the switch is very short (and the issue of battery load leveling is reduced).

So far, this system has worked really well. We spent last week camping in the Florida Keys, about a 6 hour drive each way, and the new system worked perfectly. My wife loves the new fridge... the freezer part is almost as big as our old fridge was in total. I can stock (almost) all the beer I want and she's still got plenty of space for food!

This was quite a bit of work, and I'm not done ... more battery capacity will be required for off grid camping, and I'll have to think about solar. But ... so far so good!

Comments and questions are welcome!
Dave

[creativepart]

Dave… didn’t the alternator in your motorhome already charge your house batteries when driving? I don’t understand the need for this switch between house and chassis battery at all.

I was confused by the choice of the Aims inverter, but I see it costs about 50% of the cost of a Magnum, Xantrex or Victron.

[VelocityDave]

Hi Creativepart,

No - at least in my case, no, the house batteries are not charged when the truck engine is running.

The easy way to check this is (at least in my case) is by checking the "house" voltmeter. Mine allows me to check the voltage of either the house or the truck batteries.

To check: With the truck engine running, the truck battery is at 13.x volts, and the house batteries are at 12.x volts. With the engine off, both battery systems are around 12.x volts. With shore power hooked up, the house batteries are 13.x volts and the truck battery is 12.x volts.

With the new switch turned to connect the batteries, obviously, they read the same.

Re. inverter choice; again, a big draw for me was the fact that it contained automatic switching and battery charge features. That made installation much easier.

Good luck!
Dave

[creativepart]

I don't know about year 2000 Suncruiser models, but from what I do know about all later Suncruisers is that they all were set up to charge HOUSE batteries right from the factory. In fact, we see complaints here all the time that older Winnebago gas motorhomes are set up to charge house batteries only and folks install modifications to get them to charge the chassis batteries as well.

Your set up certainly sounds like there is either a problem with your BIM OR a previous owner changed things.

Again, I'm not totally dependable on info for coaches yours age. But I did look up your models wiring diagram and see a typical set of battery solenoids that connect the alternator to the house batteries. Also, these OEM solenoids do the connecting/disconnecting automatically that you are attempting to "remember" to do.

You have a momentary switch on the dash to bridge the two battery banks together for help starting the coach when the chassis battery is low don't you? If you do, that would indicate that it's the chassis batteries that should be charged by the alternator.

About the inverter - auto transfer switch and AC Pass-Thru are all common features in Magnum, Xantrex or Victron inverters. And, they are all available with or without chargers. I bring up these other brands because you tend to see them being used in RVs much more than Aims. However, Aims is a good bit less expensive. Does it have detailed info in remote displays or bluetooth apps, etc?

[VelocityDave]

Originally Posted by creativepart

I don't know about year 2000 Suncruiser models, but from what I do know about all later Suncruisers is that they all were set up to charge HOUSE batteries right from the factory. In fact, we see complaints here all the time that older Winnebago gas motorhomes are set up to charge house batteries only and folks install modifications to get them to charge the chassis batteries as well.

Your set up certainly sounds like there is either a problem with your BIM OR a previous owner changed things.

Again, I'm not totally dependable on info for coaches yours age. But I did look up your models wiring diagram and see a typical set of battery solenoids that connect the alternator to the house batteries. Also, these OEM solenoids do the connecting/disconnecting automatically that you are attempting to "remember" to do.

You have a momentary switch on the dash to bridge the two battery banks together for help starting the coach when the chassis battery is low don't you? If you do, that would indicate that it's the chassis batteries that should be charged by the alternator.

About the inverter - auto transfer switch and AC Pass-Thru are all common features in Magnum, Xantrex or Victron inverters. And, they are all available with or without chargers. I bring up these other brands because you tend to see them being used in RVs much more than Aims. However, Aims is a good bit less expensive. Does it have detailed info in remote displays or bluetooth apps, etc?

Thanks much, CreativePart - I appreciate your input.

Yes, I've got the relays, and I also have spent time staring at the wiring diagram (at least the one I have). Yes, I also have the momentary switch on the dash.

But here's the thing; direct measurements don't lie. Using the house voltmeter to measure the voltage of the chassis battery and the house battery proved to me that there was no configuration where the battery voltages were the same (as they must be if they are really connected together in parallel). I tried it with the motor running, with the motor off and the momentary switch pressed, with the motor off and shore power connected, etc.

Only when the motor was off and with shore power disconnected were the chassis and house batteries within even a volt of each other (and even then they are different enough to show that they are clearly not connected).

So, it's possible that the relay/contactor system has failed. I didn't try to diagnose that. I can turn the 12V house system on and off with the factory switch mounted by the entry door, and I clearly hear that contactor make when I do that... so clearly that contactor is making. But, under no conditions could I make the two battery systems connect into one.

Perhaps I should have tried to diagnose the contactor (relay) system, but the diagram I have is not very good, and I took the easiest path to my goal.

On your question re. if the AIMs system has a remote display, bluetooth, etc., there is a remote display available at an additional price. I chose not to purchase that (at least for now). And, yes, cost was the main factor in my decision, although in all honesty, I didn't spend a great deal of time reviewing Magnum, Xantrex or Victron inverters. Perhaps I should have, but again, the price was a big deal.

Thanks again for your input, and I'm ready to receive more! Much appreciated!

Dave