Sounds to me like you may have overcharged your batteries. I have had the same type of situation twice with both being dead batteriesdue to overcharging. Take your duel setup out and hook up a couple of different batteries and see what happens...
I have destroyed two sets this way....two 110mah and two 50 mah..both in modified Zip-Zaps..one with a Motorworks PCB and the other with a Microsizer PCB..
worth a try anyway.....
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