I have one of the few avalanche beacons that have separate modes for alkaline and NiMH batteries. (Specifically, the Barryvox Pulse.) My understanding is that

I have one of the few avalanche beacons that have separate modes for alkaline and NiMH batteries. (Specifically, the Barryvox Pulse.) My understanding is that "alkaline mode" measures the voltage to determine charge level, as one would expect. The "NiMH mode" instead uses a timer-based approach to estimate charge level due to the different discharge curve.