NEVER charge a battery higher than 1C (that is, if the battery is 1,000 mah, don't charge it above 1 amp). The battery should be at least 2,000 Mah to charge at 2 amps.
If it was sizzling I'd say there's a good chance you damaged some of the cells.
Also, if it was a battery that came with an airsoft gun, it was probably a cheap battery. Spend the $40 and get a good battery.
"Someone in a Prius tried to race me at a stop sign the other day. I couldn't believe it. I had him for the first 100 feet or so but I can only walk so fast."