Edge 530 battery drained overnight, sticky buttons

Yesterday morning I powered off my Edge 530 (held the power button and chose power off).  Battery was at 85%.  This morning when I tried to start it up for my 3h ride, the unit wouldn't turn on.  I tried for a while to reset it but no luck.  When I hooked it up to the computer later, it showed a battery symbol with a lightning bolt and then after a while it powered up and showed 1% battery.  So the battery drained overnight in power off mode.

Did I do something wrong when I powered it off?  Has anyone else experienced this?

I'm also finding that all the buttons are a little "sticky".  Not just the back button.  I have to be very precise when I click them and sometimes have to jiggle them a bit to get them to pop back out.  Maybe the power button got stuck in that way, causing the battery drain.

Other than that, the unit has been fantastic.  It's my first Edge and I got it mostly for the radar display.   Up to now I've been using Forerunners for many years.