Sounds like the charger unit you tried may not have been compatible after all. Was it 5 DC, as I said it needed to be? The polarity may possibly have been wrong. Did you check it with a meter before you plugged it in??
If it now is damaged and can only work on batteries, that should still be okay. Batteries will last a heck of a long time. I've used NiCad rechargeables for the best part of eight hours continuously powering two or more power cars at the same time without any problems. Duracells should last much longer before they need replacing.