As was stated, I bet you charged a mini battery at 2A. You can't ever fast charge ANY batteries, it's just not possible, it kills the battery.
Your voltage has nothing to do with the amperage that you charge a battery at, it only changes the voltage your charger needs to put into the battery.
Don't charge a battery at 2A unless it's 2200mah or more.
Pick yourself up an intellect or Elite NiMH battery pack