I would try a long mains recharge before anything else. Charge the device until the little red light goes out.
See this thread:
https://www.mobileread.com/forums/showthread.php?t=21337
New readers take a while before the battery meter calibrates accurately. I rarely charge via usb any more, but use either a sony recharger or a psp charger.
ND, the sliding switch is fine but the device will still use a small amount of power in order to conserve its settings. It will take about three weeks to drain a full battery. A complete shutdown is best if you aren't planning to use the reader for a while.