Melted another set of Tenergy packs today but I'm getting better. Never had to use the tennis ball this time. Timer on my DX-7 is set for 4 minutes. Got out my NiMh instrurction sheet from Dave Thacker of Radical RC. I forgot all that stuff when I went to LiPo 3 years age. Dave says first charge is C/10. I bought a Hobbico Multicharger several years ago that slow charges up to four batteries using switchable rates between 10-500 mA. His calculation is C x 1.4 divided by charge mA = charge hours and the actual charge rate cannot be higher than 1/10C. For example, I am charging a 3000 mAh 6 cell NiMh at 250 mA (1/10C would be 300 mA) on a timer for 17 hours. Calculation is 3000 X 1.4 = 4200 divided by 250 mA = 16.8 hours. If the charging hours turns out to be less than 14 hours, the charge rate will be too high and if left unattneded on a non-peaking charger overheating will result. Over 14 hours will not cause overheaing. The result of slow charging is to fill up you pack up and all cells should theoretically be balanced as far as voltage is concerned. At this point you can now fast charge your packs. I actually used an automatic timer that turned the charger off after 17 hours.

I believe my cells were out of balance and the low voltage cells overheated under load.