You'll want to check the volts. If the voltage drops beyond a certain level, things go south in a hurry. Not knowing what kind of battery you're talking about makes it difficult to give a specific answer. For receiver batteries, you'll want to use a loaded tester, such as an expanded scale voltmeter. This will check the voltage under a small current load (say, 300 mA). This gives you a more precise measurement of what's left in the battery as compared to just checking the latent voltage. Don't know much about lipo's--which you may very well be talking about with that kind of amperage.