The battery is unique to BMW units. (Or is, in the case of the Nav5).
If you aren’t riding in winter, and don’t use the Nav in the car - charge it up, take the back off and unplug the battery.
That's a good idea. I'll do that.
Given the weather, lockdown and that I'm working from home, I'm not using the bike and using the car instead when I need to make a trip to the supermarket