What does this have to do with Sonos?

Sonos used to sell iPort xPress keypads, though they now appear to have been discontinued. I have 4 of them. Battery life is typically a month or three in normal use.

It seems bizarre that attaching a keypad to a metal plate would make any difference. The magnet is in the back of the keypad. I’ve never used the supplied plates but have attached a keypad to a metal lamp stand without incident. 

I never had an iPort xPress in my hand. Is the magnetic plate an extra attachment to the unit?

I wonder if the attachment scheme mechanically distorts the unit, causing some sort of internal connection that discharges the battery. Could one of the buttons be partially pressed, causing battery discharge?

The unit should be connected to the network briefly, it it is ON continuously something is obviously wrong.

I would be tempted to physically distort the unit by placing it on a slightly irregular surface (much less than a millimeter) then press on the corners and watch for some sort of reaction. I’m not trying to break the unit, just stress it a bit.