What I can find is that the technology difference is the transmission type. The only ‘sales’ point is “BlueTooth”.
Since the same sensor is used, I must assume that the transmitters are the same size and fitted with 2 batteries in each to provide the circuits with 3 volts. Apparently G5 uses larger batteries and is hungrier than I thought.
G4 uses 391 size battery - 2.1mm x 11.6mm, 1.55 v @ 55mAh
G5 uses 389 size battery - 3.1mm x 11.6mm, 1.55 v @ 80mAh (ie 160mAh in 2 transmitters)
(Good research, when I attempt replacing batteries in a G4, I will try fitting with 389s.)
Therefore; assuming that 2 G5s will last 6 (or even 10 to 12) months while 1 G4 lasts same amount of time, the G5 uses 3 times the power of the G4. (My experience of average 12 months with G4 would then indicate G5 uses 6 times the power.) Similar to my truck using 3 times the amount of gasoline that a compact might use to make the same 200 mile trip down the road.