My first one didn’t hold much of a charge, and would never charge up past 82%. I called, got RMA (same day) with UPS tage, shipped it back and had a new on in about 10 days from first call. New one works better.
In my limited experience with this, I’ve had much better luck charging using “mains” (ac power) usb charger (I have several and all work). Also, when you plug in the charging cable the player powers on. I turned it back off, thinking this was better for screen, etc… The player would never fully charge. Now I just “stop” playback and leave the player on while charging and it goes to 100% pretty fast. The screen turns off anyway (per your settings). It will stay “on” if you are connected to your computer and computer is on, too (shows the “connected” screen and that stays on).
Try an A/C usb charger. Leave player on while charging. See if this helps. If not, you can easily get a replacement—SanDisk ws great on the phone.