That must be incredibly frustrating – sorry if I am guilty of rubbing it in – just like others trying to share experience and knowledge of the car.
I have never needed to do this myself – but I have read that waiting until the battery is almost empty ie down to last 2o or less miles and then charging at a slow rate (3 pin plug) is suppose to help recondition battery – at least then you have tried most things and are in a stronger position to complain – however with the shortage of cars I’m not sure what options Motability could offer.
Very unfortunate and frustrating.