Battery drain and charging - off grid

KGs2108DS · 08-24-2022, 07:57 AM

2018 MicroMinnie 2108DS - lots of off grid camping. No solar. Use Honda EU2200i generator to recharge. 115Ah 12VDC deep cycle battery. on-board battery charger is 6amp per owner's man. Began to notice that battery not carrying trailer through the night. Battery test OK w/load. Delved deeper to find formula for time required to fully recharge is MUCH longer than it takes the on-board LED light to show full charge, like 6+ hours, so running generator 2hr in evening and hours or so in the AM is not recharging battery! Considering: 2nd battery in parallel $120, adding on-board more sophisticated battery monitoring system w/bluetooth $209, 10amp smart batt charger connected to batteries and plugged in when generator running $100. where to start? seems like 2nd battery may be best, 1st option? But then I still end up with two batteries not really even close to being fully charged with current generator run time, especially after 3-5 days off grid. thoughts? suggestions? options? THANK YOU!

**creativepart** · 08-24-2022, 08:49 AM

Kind of all of the above.

First, I'm sure the 2018 Micro Minnie 2108DS's built in charger is bigger than 6 amp. I would guess it's closer to 35 amp. Where did you get that 6-amp specification?

Second, 115Ah 12v deep cycle batteries are few and far between. They exists but they don't cost $120 they would be much more. Trojan makes one and it's over $250. And I'm assuming you are talking about Flooded Lead Acid not AGM because they cost a lot more. The thing to know about FLA batteries is they are slower to recharge.

Third, adding a second battery will get you through the night better but as you say will take more time to recharge.

Fourth, A shunt-based battery monitor is pretty much manditory if you want to boondock and know the true state of your battery charge. The Victron you refer to is great - but you can get the less expensive version without a display monitor and just use their smartphone app. The Victron SmartShunt coast about $140 and has bluetooth for monitoring via their app.

Fifth, your onboard battery meter is pretty bad at providing your battery's actual state of charge, as you're finding out. The reason is that while charging the voltage you see is the battery charger's voltage, not the battery's voltage. And, when you stop charging there is a residual surface charge voltage that looks high but if you put any load on it the true voltage will show and it will be much lower.

Here's my suggestion of how to proceed in your situation:

First would be to get a higher amperage charger for your RV converter/charger. Usually you can remove your currant charger (leaving the converter) and put in a newer more powerful charger - I'd look for 45 amps or even 60-amps. This is about $150 to $250 depending on the number of amps. This will push more currant into your existing battery faster. But remember, the closer you get to fully charged the slower your charger will be able to charge. That's a function of increased resistance in a battery as it nears full charge.

At the same time, get a Shunt-based Battery Monitor to know your battery's true state of charge.

Adding a second battery, wired in Parallel with your current battery is the best way to increase longevity for loads overnight. But here you need to be careful. The two batteries need to be the same - same amp hours and the same age. If your existing battery is less than a year old and not had a hard life then you can add a second. But it your battery has a few years on it and hard use then adding a new battery will only tend to make your new battery just as depleted as your old one.

If you want to spend bigger money then consider LiFePO2 battery to replace your existing battery. Lithium Iron batteries charge MUCH faster, allow deeper discharges without damage and have significantly more charge cycles. These are priced between $550 and $950. Cheaper ones exist but may not be reliable.

There are other strategies you can look at - like improving the charging capability of your tow vehicle when towing. This can be done a couple of ways. The simplest is replacing the wiring from your alternator to your 7-way receptacle. The OEM thin gauge wiring in your truck has too much loss between the front of your truck to the back of the truck and as a result not a lot of currant is applied to your TT's battery as you drive.

Morich · 08-24-2022, 09:04 AM

One of the big first ideas on batteries is that they are designed to be slow. You can take the charge out much faster than it goes in and anything done to speed the recharge is likely to shorten the battery life.
Second is that the charge level is often not correct as it is taken at the posts, not down through the whole battery, so very prone to being higher than actual fact.

Some very basic reasons may help understand what you are seeing.

When we charge a battery it can be compared to putting black ink into a hole at the top of a barrel. We add some ink, look in the hole and say we have a barrel full of black water, but if we come back in a few hours and look again, we see no black! The same amount of ink is still in the barrel, just spread out through all the water instead of only at the hole where we put it in.

When we charge a battery and stop when the charge shows full, it is much the same as the barrel and we are seeing the results of the charge which is still very much just at the posts, not spread out through all the chemicals in the battery.
It takes time for the reaction to move through all the cells and all the chemical, so that takes time or we have to overheat the battery which boils off the water and often kills the battery!
Changing batttery types is one way to go but that involves lots of extra including expense!
How much extra is worth it is a decision each have to make as we study out what it requires. A second battery is as far as I've gone but others go for the whole change.

**creativepart** · 08-24-2022, 09:04 AM

Here's probably what's happening. Let's say you are arriving at your camping destination with a fully charged battery. That's not likely, but it's probably pretty close.

Then you use X amount each day. Only you know how much you are using. Then you run your generator a little and see something like 13v on your battery volt meter and think it's all recharged. But it's not at all close to recharged.

Then day after day you go through this routine and your battery's state of charge gets lower and lower and lower.

This is common usage all too often, but it's also the common way that you damage your battery each trip so it is less capable and eventually ruined much too soon.

KGs2108DS · 08-24-2022, 09:22 AM

thanks so very much to you all - great info, lots to think about! info re: onboard batt charger is from owners manual p6-2, "The on-board battery will gradually be brought to a full charge and maintained by the 6-amp battery charger...", so it appears to me that it is a 6amp charger. I may have misspoken re: trailer battery - it is 27MFDC 115 AH / MF Deepcycle, $109., purchased 10-21-19, and I've tried to take good care of it. had it load tested early this spring and it was good. My struggle with the battery monitoring system is, so I know the exact state of the battery. Being a science guy, a curious George, I do appreciate knowing those exact details. But that doesn't solve the problem of inadequately charged battery(ies). So, given limited $ I'm prioritizing on $ for solution vs diagnostics. My tow vehicle is a 2015 Trundra Crew Max w/Towing package. I do not know the size of feed to 7pin, but it does seem to bring the trailer battery to full charge with a few hours of driving. I will ask my Toyota dealer about the wiring. Yes, I also posted about portable solar option, and I'll go to your answer/thoughs there. thanks again. this is VERY helpful!

KGs2108DS · 08-24-2022, 09:44 AM

One more thought, to your earlier point, I guess, without the battery monitoring system I really do NOT know if the Tundra, during towing, is bringing the battery up to full charge. I just know it's at 12 VDC. so, guess I really do need to further investigate the battery monitoring meter. Question: I noted in the pass through compartment, just beside the master switch, a removable panel accessing the Murphy bed from underneath. in the interests of not having to run wires into the trailer cabin, I've thought of mounting the gauge here, very near the main battery cables coming from the battery box. Bluetooth would be nice, and I really like the victron gauges, but still, I can check a non-bluetooth gauge in that location rather easily, albeit needing to go outside. would other gauges that pair with cell phone work in a place with no cell service (mostly that's where I camp). BTW I carry a Garmin InReach explorer+ for comms - has worked well.
thoughts?

**creativepart** · 08-24-2022, 10:01 AM

The thing with towing - and your Toyota dealer will not help you with this - is that truck manufactures use a light gauge wire between the alternator and the 7-pin. Over that long of a distance the currant loss is pretty dramatic. Look around on the internet and you'll see folks claiming it's 10-amps or less. But your alternator is capable of 4 times that much amperage. Again, not a dealer modification, but one some owners have taken.

It's best to be familiar with battery voltages. A fully charged 12v battery is 12.7v. Your charger and or alternator will apply much more voltage between 13.5 and 14+ volts. Let say your battery is 50% discharged, if so, then it's around 12.1 volts. When you are charging via shore power you'll see that 13-14 volts on the TT's battery meter. So you have no idea what your battery voltage is. In fact, to know you need to turn off all charging and wait hours before the battery meter will reveal the battery's true voltage.

The Victron places a shunt between the TT's negative loads and the battery's negative terminal. It measures all current into and out of the battery. So, it gives a state of charge (SOC) in percentages and it doesn't care if you are charging or not.

The Victron 712 BMK is great but Victron found many were installing it with the meter tucked away and just relying on the Bluetooth and the smartphone app. So, they released the SmartShunt that does away with the monitor. It's up to you. With Bluetooth you don't need cellphone or internet access to connect your cellphone to the device. The app doesn't need internet to work.

Here's a battery chart for you to get an idea of SOC of your battery via the voltage meter inside the TT.

**creativepart** · 08-24-2022, 10:10 AM

One more thing. With your flooded lead acid battery each time you deplete it below 50% SOC and not fully recharge it only to discharge it the next day to 40% SOC and again on the next day maybe take it to 30% SOC you are shortening the lifespan of the battery. Doing this often enough and it will ruin a battery after a year of this abuse.

It's pretty much a standard that you should try to use no more than 50% of your batteries SOC on anything like a regular basis.

So, if you have one 115Ah battery then you really only have 57Ahs available for regular use. This is why adding a second battery of the same age and the same amperage will double your available amperage from 57Ahs to 115Ahs.

A key to long battery life is not only using only 50% of it's available amp hours but more importantly to recharge the battery to fully charged as soon as possible after extended use.

KGs2108DS · 08-24-2022, 10:13 AM

thank you! once again, wonderful actionable info. So, I think the point of the colored chart is that voltage is almost worthless as an indicator of battery capacity. And re: the battery monitor - is it OK to mount it in the area I described, and pair with my cell phone via bluetooth? you seemed to imply that bluetooth was not satisfactory, but isn't "pairing" relying on bluetooth?
thanks again!

thataway4 · 08-28-2022, 04:37 PM

The bluetooth pairing is an excellent way to read the battery voltage, state of charge, amps in and out. The smart shunt is a cheaper way, than the Victron 702 or a 712. All work. But why not use the cell phone if it is with you all of the time?

BobC · 08-28-2022, 05:25 PM

I'm a bit late to this party, and you have some good advisors, but I do have a couple of comments. Voltage isn't "almost worthless" in measuring SOC, it just needs to be measured properly, several (6 - 24) hours after being removed from all loads:

https://www.altestore.com/diy-solar-...ate-of-charge/

I couldn't find any listings for a 27MFDC 115 AH / MF battery but I doubt that it's a true deep cycle battery. It's more likely a Marine/RV dual purpose battery that's a compromise between a starting and deep cycle battery. A true deep cycle battery won't have cold cranking amps (CCA) in it's specs. In any case, the general consensus is that pairing a 2019 battery with any new battery isn't a good idea.

Have you tried charging your battery with a good, external battery charger overnight until the charger says it's at 100%? If you do so, you can then check it's SOC as detailed in the above website after a suitable no-load rest period.

dickb46 · 08-28-2022, 06:15 PM

I'm thinking you aren't getting enough charging first off. The 2200 watt generator should be able to charge your battery in a couple of hours.
I carry a Schumacher charger, it's advertised as a 100 amp charger but that's "engine starting" rating. It will actually charge batteries at 30 amps or selectable 30/6/2 amp. After parked for 3 weeks it will bring my 2 chassis batteries from 12.2v to 12.7v in 3 hours.
Getting a good charger would be my first fix while you decide what you want.
I got this charger 8 years ago at Walmart, it was under $75 and weighs less than a case of beer.

dickb46 · 08-28-2022, 06:25 PM

That's a case of "cans" lots of difference in weight there.
LOL that was dw's input

KGs2108DS · 08-29-2022, 11:01 AM

Good morning: success in installation of Victron battery monitoring system! Already getting clear idea of how valuable this data will be! thanks again! I have some pics of the installation, as well as screen shots of data, but have never figured out how to add a picture from my iPhotos.

mff3429 · 09-01-2022, 05:41 PM

Just an additional thought. When I had battery problems and went to an Interstate Battery location, the owner described that to know the state of charge, one really should use a temp-compensated hydrometer that measuress the specific gravity of the battery cells. (One could locate a bad cell that way I guess, too) See: https://www.freeasestudyguides.com/b...vity-test.html