I have one but haven’t used it to diagnose any issues. Most common culprits of battery drain are accidentally bumping the shifter when the bike is leaned to the derailleur is pushing to shift constantly. Having the limit screws too tight so the RD shifts right to it and keeps pushing instead of relaxing. The other one I’ve seen is having the wireless adapter that let’s you connect the system to a Bolt or Garmin head unit. Sometimes it can get stuck in pairing mode and drains the battery…not shutting off after the bike sits still.
I’m sure there could be a component problem as well but that wouldn’t be as common as these other issues.