Dual battery question

[dbailey1111]

I have the battery out of my old trailer and room for it on my new one. The new battery is smaller than my old one. Is it ok to wire two different size battery's in parallel. New trailer one is a interstate group 24, 405 CCA, 505 MCA dual purpose marine/RV installed by dealer. New old battery is ever start (Walmart) group 29, 845 MCA, 122 Ah.

[f6bits]

It'll work, and be better than either one on its own, but not as good as two identical batteries. The "new" battery probably isn't that great to begin with so start planning on what matched pair you'll get next.

[dbailey1111]

Thanks. What would you suggest I start planning for? I would like to have 2 group 29's but they won't fit without hanging over the sides of the tongue. What makes two identical ones better? Would 2 group 24's be better than what I have? Will having 1 battery with more CCA,MCA,Ah tied to a lesser battery be in some way over power the lesser one? Sorry just don't want to have a melt down on my week old unit.

[B&T]

You should make sure both batteries are charged before you wire them in parallel. If one is charged and the other is fairly discharged there will be a heavy current surge from the charged battery to the other one.

[Festus2]

I don't think you need to worry about a battery "melt down" having two dissimilar batteries hooked up in parallel. If they were in series, such as two 6volts, that would create a problem.

While not an optimum situation, you should be okay. The only problem could be some difficulty in that they will have different charging set points but as long as you keep both batteries fully charged, you will be fine.

At the appropriate time, I would suggest pairing them up so that they are identical both in brand and in capacity.

Relax, you will have a great holiday.

[BulletOwner1]

Theory has it that two 12v batteries wired in parallel will go bad quicker that 2 6v golf cart batteries wired in series. The two 12v ones will end up unbalanced and will deteriorate. And golf cart batteries should fit in the same space. If you dry camp a lot 2/6v is the way to go.

[Festus2]

BulletOwner1 -
I may be wrong but I thought it was the other way around in this one aspect ----- If you have 2 - 6volts in series that are of different types and specs, charging may be problematic. One will become fully charged before the other or one will get overcharged while the other is undercharged.

One disadvantage of having 2 6 volts is that, if for whatever reason, one happens to fail, you are hooped since having a single 6 volt battery isn't going to cut it.

But I agree, the only way to go if you are doing a significant amount of dry camping is to go with 6 volts --- and take good care of them! We have 2 Trojans and they are work horses!

[theeyres]

If you don't do much dry camping, one battery is fine. If you are planning on dry camping, go with the two 6v. I did that on my former trailer and the difference was amazing. That's what I am planning to do with my current trailer.

[K4BEV]

THEE problem with 2 older, different batteries in parallel is that one will be a much healthier battery than the other. Once connected they will equalize - Unfortunately the better battery will be pulled down to the lesser battery's condition. IF the lesser battery has a shorted cell (for example) it will kill your good battery eventually....

Either go with two new, identical batteries - OR - install both of your batteries but only connect the negative posts together. If your *primary battery* is depleted with no way to charge it (i.e. dry camping) then switch the positive wire over to the secondary battery and make plans to charge the other in the near future.