Was recently issued a new HTC One M8 (windows os) and initially thought the phone was a POS because the display looked...

Had a similar problem with my 1st gen UE Boom. Was researching battery swap but stumbled across a reset option. With the unit off, hold the Vol down button and the main power button for 20 seconds (well, that’s how long I did) to reset the device. Will have to re-pair it with devices (and rename it via the app if you like) but after the reset, it took about 3 hours for a full charge and battery life appears to be MUCH improved. Cost’s nothing and worth a shot…