I have two keys, the one I was using as the main (Key 1 henceforth) has mysteriously died overnight as it wouldn't open the car this morning. The indicator light is not illuminating when buttons are pushed. No warnings at all about a low battery, so I thought maybe it had become un-synced but performing the resync process as per the manual has not changed anything.   I popped the battery out of Key 1, Sony CR2025, no signs of damage and it reads 2.975V loaded which still seems healthy