mixing batteriy sizes

wa8yxm wrote:

swimmer_spe wrote:
I have 3 deep cell batteries. One of them is bigger (and newer) than the other 2. What happens if I try to use a big and small one together? What about putting all 3 together?

I hear a lot of "Stuff" like "The weaker battery will draw them down">> Bull droppings.

What will happen is the batteries will work it out.. The Ideal socialist society will be formed (Each according to it's ability, each according to it's needs)

Imagine you have 3 batteries one is 100 AH capacity one 200 one 300
You are drawing 60 amps and you meter each battery
You will find the 100 battery is putting out 10 amps. the middle one 20 and the 300 30.. They work it out. Same when charging.

NOW when batteries age one of two or three things happen and this will affect you ONE of them is "of concern"

First. The internal resistance may go up.. in that case at low current you won't notice it but at higher discharge rates this one will simply not provide as much juice.. when the discharge rate goes down it will likely provide a greater share however for a time till they balance out So this is not a problem.

The second is loss of capacity. also not a problem save the battery basically "Disappears" electrically.

Finally the only concern. A Shorted cell.

OF course this can happen with a battery that's a week old (And did to me once. what's more that battery had a lifetime warranty so the replacement was free). (Pro installed too).

And I have behind me as I type 3 batteries. all different sizes all different ages and that's precisely how they act.