I just answered a question about an airsoft battery at AirsoftForum.com from ShadowBandit12, and thought it was worth sharing.
Question: My KWA G36C has not been holding the battery's charge lately. It's not every time I charge. But others, the battery doesn't even make it through the first game. I have a smart charger and a 9.6 battery for it, and I use the smart charger to charge it. I don't know if this is due to bad connections when being charged, or something wrong with my gun. Also, the charger makes a weird noise that it did not before I started having this problem. When the battery doesn't charge it almost instantly starts die, but sometimes it works fine. I have even tried getting a new 9.6v battery. but it still did the same thing. Any suggestions about what's going wrong?
My Thoughts: I would check your charger with a voltmeter and the wire connections in the gun. Your Airsoft battery is either being shorted out in the gun, or the charger is not working and is not charging to 100% or at all. Tenergy Battery Chargers work with many types of RC and Airsoft batteries and will balance the lithium cells.