Different Brand Batteries in Parallel

Thanks for all the replies. Looks like I will be replacing both batteries (but not with Delco this time).

Thanks again for the help,
Brad

Batteries in SERIES need to be identical twins (Same make, model, size, shape, age, and so on)

Batteries in PARALLEL need only be the same type,, IE: Flooded wet cell, Maintenance Free, AGM.

HOWEVER it does not hurt if they are identical in other ways as well.

I run a mix of make, size, and type here.. (Type is not recommended) (maintenance free and Flooded, Used to include AGM in the mix too but they died young, very young, (And were isolated from the rest at the time).

I would not worry about mixing in parallel.

One "Danger"

If you have a smaller and a larger battery and one of them develops a shorted cell (Which by the way happened to me) in theory it can draw enough power to overheat and "Explode" or even catch fire.

Here is what I have

Three Group 27, one of which had a shorted cell, and a pair of U-2200 Golf Car batteries.

IT did not over heat, It did not explode,, It just drew power less than what the converter put out so if I lost 120 volt the inverter cut out in like 10 seconds or so.

I replaced it about 1-2 weeks ago

Yesterday I tripped the 30 amp park breaker.. Did not know it for some time (I have an indicator light that was dark) THe inverter held no problem.

So even though I preach that danger..... I did not get "Bit" by it.

There is no need for the batteries in parallel to be of the same capacity if they are both in good shape.

However, if by that is meant that two same- rated capacity batteries are now of different capacities, so that means one is more sulphated than the other, then yes that will be problematic.

Bill.Satellite wrote:
They don't necessarily have to be the same brand, but as mentioned above the do need to have the same capacity with also means they need to be the same age. If one is gone, you need to replace both.

Ditto the above.

You can parallel lead/acid batteries. You will not get a capacity that is the sum. You will get less. The possibility of a battery explosion goes up remarkably with batteries in parallel. If you feel you must parallel LA batteries as your only option, then go ahead, but if they are not separated to charge or store, be ready for the fight.

Matt

YES you CAN replace an old completely different 12 volt battery when running in line with an older battery. The older battery will be weaker due to age and it MAY draw the new battery down to it's level. Result will be that you won't gain as MUCH benefit of having two batteries paralleled as you COULD have but it will still work. If they are different ENOUGH you may also have the same issue in charging them and one may not ever be fully charged.

In a perfect world having two new batteries is better than having one old and one new - but it's not a perfect world. Over the years I have had a battery go bad and didn't replace both because the other was still in good shape - never experienced a notable difference.

OP, even if they are not within 0.1 volts of each other and since it's in a boat... once charged, do not store them hooked together. You probably already have one of these.

I would not mix battery types
---------------------------------
I agree, and forgot to mention that.
But it is well known that different types, carry different voltages
But then again, how many MHs are charging a LA starting battery, and AGM house batteries together in parallel ??

RJsfishin wrote:
Capacity make no difference whatsoever ! A group 22 will run perfectly w/ a group 31, or even an 8-d.

Brand makes no difference,....as if a 12v system knows what brand a battery is !!

Age in itself doesn't make any difference either, only that age usually coincides w/ voltage.

As Ivylog said, its all in the voltage. The closer the voltage is between paralleled batteries, the better. But even then, only to a point.

The problem is that the internal impedance of different battery types varies considerably as does the internal impedance of the same battery types but of different ages.

The batteries varied internal impedance does not allow for equal load sharing nor does it allow for equal charging levels and can therefore cause damage when high currents flow.

Plus, the batteries will have circulating currents between them which wastes energy due to losses within the internal impedance (extra heat and boiling).

I would not mix battery types or batteries with significantly different ages.