The battery was approx 50% charged when I removed it.
BTW...I have tested calling the cell/mobile while it is in the bag.... many many times. It never failed to block calls.
IOS or Android device? New or old?
Likely that phone shut itself off to preserve the batteries, since it couldn’t find a signal.
After all of the complaints about short lived batteries, not surprising to see phone makers become aggressive to preserve a batteries life.
Or, not sensing a signal, the phone shut down so that when it was discovered, there would still be some battery life left to start a reboot.