Bat monitor (second battery) "battery_usedmah2" value is nonsense.

Bug report

We have 2 individual batteries in a setup. Both on their indivudial (mauch) sensors. Connected to port one and port two. Parameters are all identicall. Voltage and current valueas are correct, however battery_usedmah2 on the second battery is show is strange number. See screen capture below.
**Issue has been investigated on Mavlink/Arudpilot side and was found the data there was correct, so most probably Mission Planner bug.**

See original issue on AP: https://github.com/ArduPilot/ardupilot/issues/8974#event-1748446363

Arduplane 3.10 latest beta
I do not think it is a version problem, we never tried it before and I dont think many people would either. As I said the other values are correct. This is a calculated value I believe. So hardware even is irrelevant.

Platform
[X] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover
[ ] Submarine


Start by reproducing the two-battery setup in Mission Planner and inspect the displayed battery_usedmah2 value against the correct MAVLink data described in the linked ArduPilot issue. Done means the second battery's calculated consumed-mAh value matches the source data without affecting the other battery readings.

Written by the indexing model from the issue text.