[BrianG]

Any battery will have a limit as to how many amps it can supply on a continual basis without overheating. AFAIK, LiMn was "safe" against explosions from puncturing, but you can still pull more current than the C rating and ruin them. Even though they aren't Lipo, they still have a C rating you have to follow.

You can measure the voltage on each cells in a pack by using the balancer connector. Just measure across each pair of wires. For instance, let's say you have a 2s pack; it will have three balancer wires. Let's call these wires wire1, wire2, and wire3. You can measure one cell by measuring across wire1 and wire2, measure the other cell across wire2 and wire3, and the whole pack by measuring across wire1 and wire3 (or the main power connector).

What do you mean it won't work with the balancer? Does the balancer display some type of error or something? What happens if you try to hook the suspect pack on a charger without the balancer (just as a test)?

I suppose you could measure both packs with a micrometer or precision ruler and compare the dimensions.

BTW: Before you hook up any battery pack in parallel with another, you really should make sure they are the exact same voltage. If they aren't the same, or very very close, you will have a potentially high current flow between the two packs, which could cause problems.