Originally Posted by petefoss
I beg to differ but in parallel you would be fine with different size batteries. As soon as you connect them they are at the voltage. As you draw from them the current with split automatically so they drain together.
In series two different capacities would be very bad but in parallel they should be fine.
They may be "at" the same voltage since they are physically connected in parallel, but it doesn't mean they are generating the same voltage, or that he current drawn from each battery will be proportionate to its capacity, nor charge proportionately to its capacity. Putting two different capacity batteries in parallel is not standard or good practice for a reason.