I can't comment on the 540 or 840, but I use the 1030 plus with the Garmin IQ app "Ebike Field". For my Creo this shows both the power assist mode as well as the total battery level for the main battery and RE battery combined - as a percentage. As I always use both batteries being 'drained' simultaneously, this works very well for me. I haven't yet tried using RE battery draining first and seeing what the 'Ebike Field' display shows.