Most RC hobby chargers will do this. They have charge/discharge cycle and discharge/charge cycle capability. So, if you want to find out the amp hour capacity of a module, this is a fairly foolproof way. And generally speaking, it's not a quick method because it takes quite some time to discharge a fully charged module to empty. The Gen II Prius individual battery module replacement thread by ryousideways is the best place to look for details on how to do this. It's a very long thread but well worth the time. The thread lists about every type of RC hobby charger available. The reason I'm directing you there is primarily because the price of RC hobby chargers vary from $30 to $300 so one size definitely does not fit all.
You might think of a module as a jar you can't see into. You can't see what its capacity is, or even how much is in it right now. You can pour it all out, and see how much comes out (but that doesn't tell you its capacity, because you don't know how full it was when you started). But then you know it is empty, so you can start filling it. This doesn't really tell you the capacity either, because charging a module isn't exactly like filling a jar; there are charging losses, so you pour more in than what ends up being in the jar. But you can tell when it's fully charged, and then you can pour it all out again and measure what comes out, and now you know its capacity. The typical hobby chargers can do most of that for you automagically. -Chap
