Is Bluetooth battery information readable in Windows on Boot Camp? Is there any way to see the battery level of a Bluetooth device (e.g. magic mouse) in Windows with Boot Camp?
There is an application for Windows called "Bluetooth Battery Monitor." It is in beta right now, but I use it for my Ghostek SoDrop 2.0 headphones, and it works well. 

You can download the beta at: https://www.bluetoothgoodies.com/

I don't think that BootCamp per se would make a difference as to whether the Windows program would work or not, or any program at all, for that matter.