Just finished mowing our lawn and usually there is about 1/4 power left in the battery when I put it on the charger. This time, however, the charger indicates the power is at 100%. This is very unlikely. I've disconnected the charger and reconnected it with the same result. It's the charger that comes with the new self-propelled mower. I do have a secondary charger that came with the trimmer that I could use. Any suggestions about this issue?