It could be one or more of the cells are bad. Assuming you didn't reset the charge timer in the scanner, what are you plugging the scanner's USB cable in to? I plug into a wall outlet (mains for any lurking Europe friends) using an Apple USB to 110v adapter "cube" meant for iPhone charging. These are known to provide close to 1A reliably (unlike the knockoff ones which can kill you). Once I charge for a good 7-8 hours if I check the battery voltage (momentarily press the multifunction control on top while the scanner is on) I see a bit over 4V or so, maybe as high as 4.3V. Arguably a bit high for rechargables, but more importantly is that the value is roughly consistent each time I charge.