Connect batteries in parallel

[rderito]

Hi, is it OK to parallel connect a 12 volt 80ahr agm battery to a 100ahr agm battery? they are both a year old and in like new condition. and if its OK which battery terminals should I connect the charge controller to, one of each battery or only the 80 or the 100. I am using a 40amp mppt C.C. with 320 Watts of solar.
Thanks

 

[picopat]

Hi, is it OK to parallel connect a 12 volt 80ahr agm battery to a 100ahr agm battery? they are both a year old and in like new condition. and if its OK which battery terminals should I connect the charge controller to, one of each battery or only the 80 or the 100. I am using a 40amp mppt C.C. with 320 Watts of solar.
Thanks

It's ok to connect them in parallel but it is likely that one battery will do most of the work and wear out faster than the other.


Before you connect them make sure they are charged to the same voltage to avoid large currents that could occur when the higher voltage battery sends charge to the lower one.

You can balance differences in the wiring by connecting to your system using the positive terminal of one battery and the negative terminal of the other one. This balances differences in the wiring but does not help with the differences in the batteries themselves. So to be clear, you connect the batteries to each other (+) to (+) and (-) to (-) to make the parallel battery bank, then connect that parallel bank to your charge controller & loads using (+) on battery 'A' and (-) on battery 'B'.

Patrick

 

[B and C]

^^^ Good advice so X2

 

[tx2sturgis]

Yes it will work. There is little 'real world' difference between a good 100 ah battery and a good 80 ah battery when they are relatively new and in good condition. 

Be aware that if you consistently draw them down (high discharge) during heavy use, and over a period of months or years, the smaller battery may 'age' sooner, recover slower, and have less reserve capacity, which will in turn lessen the overall life of both batteries to about the life of the smaller battery.

But yes, it will work fine.

 

[rderito]

Thanks for the answers