Controller trouble...

[Sleeping911]

I have recently fried not one but two 49 mhz controllers...i have not fried the cars as they still work on another controller. What i have done is installed a universal adapter plug, soldered it into the controller battery terminals and remain to charge my single cell ZZ off the controller using 300 ma @ 3v adapeter. The only thing i think i might have done is i built a stand alone charger and read that you could charge at 4.5v, maybe i left the adapter at 4.5v and plugged it into the controller with the batteries in it ....would that have fried it? However i didnt make this mistake on my previous controller, that controller i left plugged in for a couple of hours using my 300ma @ 3v charger turned off, went to bed, woke up next day and didnt work. Is there any way i can fix my controller. Is it that the controller can only handle 3v? Any suggestions PLEASE!