How can I determine the maximum amp output of a battery pack?
Some background: I've got a 5-AA battery pack hooked up to a microcontroller and some continuous rotation servos, but there's current weirdness when everything is drawing their maximum amounts. The microcontroller randomly restarts itself, and the servos stutter and jerk around instead of rotating smoothly. Suspiciously, everything runs fine, just a little more slowly, when hooked up to my laptop's high-speed USB port, despite that being lower voltage. This makes me suspect that I'm exceeding the current output of my battery pack at 7.2V.
How do I determine how much current my AAs are capable of pumping out? Do different battery materials have different output ratings?
(I know that LiPo batteries of the sort used in RC cars have a "C" rating that represents the discharge rate, but I've been unable to find a similar rating for household batteries.)