I had a similar problem to this with my Delta diesel.
Garage said I was not doing mileage during pandemic ......
Eventually replaced battery with an uprated unit.
Took into garage - put onto computer checker and battery good, but was drying before their eyes 14.71 .... 14.XXX etc
Error code came back to the clutch system!
Elaboration: I have size big feet. In the intervening weeks when having this problem, I had somehow 'kicked / nudged / moved' a make break switch on the clutch pedal. There is no warning light - but it throws up an error code. Effectively there was a closed circuit draining the battery.
Remedy: Replace the switch* above the clutch pedal and then fabricate a 'box' to prevent it being nudged.
The *switch was ok looking from outside - but refused to open / close on examination. Stupid place for a switch was the mechanics commentary.
Has worked now for 18 months without any further problems.
Hope this maybe of use