Nicad, NiMh and Lipo batteries are very commonly used in model aircraft, model boats and model cars.
Of the 3, model aircraft are most critical because the average weight of a model aircraft is about 4 pounds and the average cost is about $500. Given that it flies in the air and can have a potentially disastrous crash should the flight system fail, many numerous articles have been written about battery care and maintenance.
Here are some links to some battery information already out on the web. Please have a read and see what you can learn. what you learn form these sites can be directly applied to your battery for your AEG, there really is no difference in terms of application and performance.
The best advice I can give you is to get a good smart charger that can both charge and discharge your batteries.
A B6 type Charger can be had for about 30 bucks on the net or about $60 at your local model hobby shop
This can charge, discharge and cycle your batteries for you, and will display your batteries performance on an LCD screen so you can SEE what is going on with your battery.