The Tenergy Smart Universal Chargers are actually substantially better than the plain old Tetrix charger. They actually use pulse and negative pulse technology to avoid the battery overheating during fast charging and automatically shut off when they are fully charged. We use these this year and we highly recommend them...and hey, $17.90 isn't a bad price either.
http://www.amazon.com/Tenergy-Smart-...harger+tenergy
Hope this helps!
Goodluck!
Bo Russell
CAD Engineer FTC #5037 - got robot?