I noticed that while I was charging batteries with the PRO-107, the bottom of the unit became quite warm. I took out the batteries and they were quite hot. I had the switch in the correct position, used the correct cable plugged into a Sony 5V 500mA power plug that accepts usb to ac. It was set in the ipod position. Sometimes when charging this way I will get a "charging complete" message and other times it just says "charging" This was the first time that I felt it get hot, but there seems to be no ill result, the scanner works great. I may keep the charging away from the scanner and do it in my charger.So far I can get more than 12 hours with freshly charged batteries. The Rayovac Hybrids have been very good. Just make sure if you are charging with the scanner to check on the warmth during this process.