The Dexcom G5 transmitter will shut off after 105 days via a software command from the receiver. But that doesn’t mean the battery is dead or that the transmitter ceases functioning. It just means that the G5 receiver will no longer accept readings from it.
So just how long will the transmitter battery last? Mine is at 123 days and still pretty strong. I’ll keep updating each week until it dies. Note that voltages and resistance are still in the excellent range after 123 days.
BTW, this is not possible with Dexcom receivers, standard or iPhone. This requires xDrip.