I wonder if it sort of tests the battery? So like instead of saying it is 100% it checks the volt output over an hour or two to decide how full it is?
Sounds better than what my Vibe does anyway. It just has 3 bars, can sit at 3 bars, then 2 bars for ages, once it gets to 1 bar it will be dead soon and you have to change it. Real pain as you don't get any real warning. It has happened during the night a few times and since a battery swap invokes the self test of the pump you have to rewind and then prime the tubing again. Worth remembering since my pump doesn't use a handset / meter that it is hard on batteries, meaning you get 4-6 weeks out of one.