Adding a 2nd battery Micro Minnie 2108DS

[KeithB]

I have had a WindyNation 100 amp-Hour 100AH 12V 12 Volt AGM Deep Cycle Sealed Lead Acid Battery in my 2108DS trailer for about two years. We plan to boondock (first time) in Colorado this summer. I have solar but it is pretty barebones. I’m concerned if my battery will hold up to the demands of running the heater at night. Question : can I add a second, new, battery to my 2 year old battery.

[creativepart]

Originally Posted by KeithB

Question : can I add a second, new, battery to my 2 year old battery.

Yes, you can. But the old battery will bring your new battery down to match its performance and condition. It’s always best to replace the old one with two new ones. But that doesn’t mean you can’t do it. If you think the old battery has had a rough life then, maybe not. But, if it’s been babied for two years, never deeply discharged and maintained really well then… it’s up to you.

[Morich]

Think of it as being two horses pulling a wagon?
If we have one old and worn and add a new fresh pony, it will work but not as well as if we have two new strong ponies!

Better not to add the seond new but then that gets into all kinds of questions that we can't really test or measure too well.
How much good is left in the two year old battery? Really tough to sort out a good sure answer!

[KeithB]

So a little more info. I have mimicked battery use in My driveway. Low temp where I live was 55 last night. I put heat thermostat on 68 for the night. When I checked in the morning the battery read 11.7. Yeah! So I turned the heat up to see how the battery handled. When the heat fan kicked in the battery read 10.5! I turn the heat off and battery jumps back to 11.5. I turned the kill switch off and battery went to 11.7. Am I ruining my battery if I run that scenario for a week? By the way. Solar panel brings it back to full charge within a couple hours. Thanks for your thoughts.

[Morich]

Battery voltage readings can be very tricky! The problem is that we are reading the results of a chemical reaction and at only the very top of the battery, while the TOTAL of the whole batteiry chemicals is important.
As we use or recharge a battery, we change the reading right at the post and the real chemistry takes hours to get worked all the way through the battery. It's a slow process, so we need to let things settle for a few hours before we can use voltage to decide how good a battery might be.
It is sometimes described as adding black ink to the hole on a barrel? If we add ink and look in the hole it looks totally black but if we wait a few hours and look, that black has moved into all parts of the barrel and we may not see much black at all.
Surface charge is often the term to look over/study to avoid being tricked!

Here on the forum, we often get reports that folks find their battery shows 13+ volts and they think it good. But what that shows is they have recently been putting a charge voltage of 13 or more as the chemical of lead acid will only go to 12.7-12.8 volts and we know that any higher is just not reliable!

A better test is a load test as it puts an load on. What you have done is a modified load test as it does remove the voltage at the post and gives an indication of how much power there might be on further down in the battery.

I wish I could give a good, firm, answer but batteries are not that sort of thing!
Just so many variables! How often they have been run really low, how old, what temperatures and even what was in the water that might have been used.

I know Olathe and you may have quite a lot of minerals inthe water? Hard water has limestone and magnesium and if we use tap water in the batteries, we can leave those minerals sticking to the lead plates and that keeps the battery from working as well as without the minerals coating things!

[creativepart]

Kind of yes, depleting the battery over and over will ruin the battery. More important even is to bring it back up to 12.7v as quickly as possible after draining it to 11.7v.

You should put that battery on a good smart charger and charge it for more than a few hours. Overnight would be good. Or if you have power at home and are at home plug in the TT over night.

When charging you'll see 13 to 14.5v on the battery meter. That's the charger's voltage, not the battery's voltage.

After 24 hours of charging. Unplug the charger/RV and don't run anything at all on the TT. Let it sit totally "off" with no power being used or any charge being added.

After another 12 to 24 hours take a voltage reading if it's below 12.4v then that battery is pretty shot already.

Setting the heater for 68 will use tons of battery power. During the day you wont need heat. At night you'll be under covers and set the heater for something in the low 60's to high 50's. That will use much less power. That would be a more real world test for the fully charged battery.

Here's the battery voltage/state of charge chart. But ONLY when a battery is not being charged or used for a number of hours - like overnight. Using your battery to the orange and red sections are ruining your battery if done often or without full recharge ASAP.

[Marine359]

If you find that you need to replace your existing AGM, it may make more sense to switch to LiFePo4. But maybe not. You can get a 200ah LiFePo4 now for $600. 2x 100 ah AGM will set you back $400. Despite what you might see posted, you CAN charge a LiFePo4 with your existing charger. But you’ll only be able to charge it to about 80% with an OEM charger because it’s not profiled for LFP. So compare being able to get a useable 160ah from a 200ah LFP with your current charger, versus 160ah from AGM @ 80% DOD (not a good thing to do if you want long battery life). It may make sense to switch if you’re planning on keeping your camper for more than a couple of years. Swapping out the charger for a couple hundred bucks would give you the full 200ah from LFP.

[Morich]

This is where my wife and I came down to it NOT being practical for us to do much boondocking. But that is very much a personal choice thing and not to argue!
Where we came down was that we were out in the "wild" all we needed without camping in it, so the cost of converting muchof the electrical versus camping at parks and sites where we found electrical hookups was just a no brainer in our part of the world.
It was also much less brain strain!
At this point, We are good with staying less "boonies" and driving a few minutes to get there ! We both grew up in the "woods" and it just doesn't give us that much more to stay there when compared to a few hours of visit!

Bottom line? We admit that we like our comforts too much to go too far away from them!