Battery Discharge when Stationary

My car is dying of a car variety of long Covid. For the first 3 years of its life it did over 20k a year, but in the last tax year it did zero business miles and since 22Dec 2019 its done not more than 400 miles and all of those driving to the bottle bank or in pointless circles around Tendring district charging the battery.
The battery seems to be deteriorating badly now. Even after a 30 minute drive today it still demanded I turn the engine back on so so I’m trying a more direct form of nutrition!