Well, i found a 2600mAH 3.8V made by Samsung. I am charging it now with mt trusty 5th gen 30 g. Oh yes, too thick. But i was looking for something to test the concept. Since I have the Samsung now I will cancel the order. I also tested a 3.6V 2450mAH thinking maybe this would work. It did not. The 30g would not even start up. I'll charge it and try again, but I think this means 3.7V is the absolute minimum.