(ET) How to tell which battery is bad.

["Perry Cain" <perry suppleye com>]

I think I have a bad battery.  My one tractor stopped working correctly.
When I tried to go forward, the tractor would just jerk and the power would
flatline hard when I pressed the accelerator. I figured I had a short
somewhere, so I left it sit till I could get to it. So I was using my 
second
tractor.

But since the batteries in the first tractor were newer, I decided to put
them in the second tractor.  Now the second tractor is doing the same 
thing.
Thus, I assume it's a battery problem.   All the batteries have a charge,
but I still suspect it is one of the batteries.

Any idea how I tell which one?

Perry Cain
perry suppleye com