Hmmmm. I wonder if this is the reason my Bontrager taillight has been acting funny. Just before a ride I turn it on. When I get home, I find it's turned off. But I can't turn it on. So I plug it in but the charging light doesn't flash and it stays uncharged overnight.

Thinking it's reached the EOL after only three years I get another taillight at half the price but with AAA batteries.

Then I check the Bontrager and it turns on again. So I continue using it and carry my new light as a spare.