My Windows phone has not been known for quick charging, but I fould out a new issue with the battery. I had the phoned tethered to my laptop for charging and downloading and used one of the USB ports that made the cable get in the way. When the phone was fully charged, I disconnected the cable from the laptop, but I did not disconnect the cable from the phone. Several hours later when I went out, the phone was totally dead. It took another overnight charge to bring it back to life.
So it appears the cable has a vampire feature and will suck the life out of the phone unless the other end is connected. This may explain previous drained battery episodes when the phone was connected to the laptop and the laptop was turned off.
John Marshall… Visio MVP Visio.MVPs.org
john Visio MVP 
Oh that’s a great tidbit of information! I have to try/test this out (under controlled environment :>). Thanks for the heads up!