Multiple Batteries in Parallel
I have several regular 12v batteries that are different sizes. Can I safely hook them up in parallel without damaging any of them?
Forum Discussion
Boon Docker wrote:
Here is a quote from "The Battery Experts"
The 100 AH battery will become fully charged long before the larger one. The combined voltage will rise, but by the time the controller turns off the charging sources, the 100 AH battery will be overcharged. Meanwhile, the 200 AH battery will not get fully charged. When the bank is being discharged, the 100 AH battery will go flat and its voltage will fall well before the 200 AH battery. The inverter will eventually cut out but not before the 100 AH battery is excessively drained.
So is the above not true?
Yes, it is not true. At the normal RV discharge and charging rates, the two batteries have plenty of time to stay even in SOC wrt the "combined voltage". My own battery bank is a pair of 100s for 200 in parallel with a single 250 (AGMs) I have checked for that.
Where you get uneven is with say three batteries in parallel where you have the load/discharge wires on the outside batteries so the middle battery is not worked as hard.
Or with both wires on one of a pair so the second is "downstream" and not worked as hard. Or if one battery is in poor condition.
I don't know, but perhaps it could get uneven if the discharge or recharge rate was crazy high, so the smaller battery could not keep up ( the chemical reaction needs enough time)
