Mine says battery always full when it can not be after 6 hrs out.
Mine has done this for several years now. I haven’t ‘charged’ it specifically for a very long time, but it’s never died on me.
The only charge it gets is when it’s plugged into my tablet or laptop to upload rides to Garmin/Strava.
Googling I did suggested that the battery can move around inside, breaking the connection.
I took mine apart to get one of the micro switches replaced (the page/menu button stopped working) & it’s pretty tight in there. There isn’t a lot of room for movement & the battery is connected to the board via a wire with a small plug on it, so it’s unlikely to be a connection issue.
Most of the issues I have had with my Edge 500 (of which there are many) seem to be down to software updates.
Mine won’t do breadcrumb trail stuff anymore because of a software update that gave me a load of useless (to me) power meter functionality.
The trail appears on dead straight bits of road, and then as soon as you get within 1/2 a mile of a turn, it will disappear just long enough for you to have no idea where you are going. Then it will conveniently re-appear on the next straight bit of road…..