im wondering if its not your charger. each charger has a chip built into it to regulate the charging. If the chip is going bad its not going to charge the battery to its maxium output no matter how many times you put it on the charger. Try using a different battery charger and see if thats the problem. My kids RC firetruck came with a really cheap charger and i charged the battery as per instructions. Well the truck ran for 30 seconds and the dead battery lite came on. Well to make a long story short. The processing chip or voltage chip was bad and had to buy a different charger..Charged the battery and the thing ran for over an hour on a single charge..havent had any problems with it. Another thing about rechargeable batteries is they can only be recharged a certain number of times before they become dead... Just a sugesstion.