I plug my BT Jr into each bike in my garage about once a month. The batteries don't drop below 80% and return to full charge within a couple of hours.

 

I plug mine in anytime the bike is going to sit for more than a couple of days. Probably don't need to, but what harm is there to always have a fully charged battery when I go out to get on it?? Just don't forget to unplug it.

 

Yep, had my BT jr. for five years on two different bikes and I always plugged em back up after each ride unless I would be leaving again that same day. Too easy not to......

And my bike sets tight to the wall, so I have to unhook before I back it out.