Are they Ni Cad batteries? If so, you might want to discharge them all the way down then do a re-charge. That helps sometimes. I used to have that problem With my R/C airplanes until I switched to NiMh batteries. I think it means Nickel metal Hydride. They hold twice the charge or more as the Ni Cad's do. You can use the same charger with both types of batteries. Not so with The Lithium batteries. Do NOT use your old charger With Lithium batteries
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