cheesecadet -- I strongly recommend running the c4s through the ps2 (while, say, recording your stereo) and timing how long it takes with a fresh battery for the low battery light to come on. Due to the variations between these batteries' capacity, I'd run the test twice.
IMHO, that's the best way to know how your gear will perform in the field, as it's no fun to have the stress of that low battery light come on in the middle of a hot jam.