Can a 'kindly off duty' Acorn Stairlift Engineer or other help please?

We have an Acorn Stair Lift (Bison 80) which may need a reset. We do not have a current service contract because of the firms high annual costs. Recently we went away to visit family for two weeks and because the lift charger tended to get quite warm my wife turned off the charger. When we returned home the charger was switched on, but clearly the batteries are not getting any 'juice'. Prior to our trip, the stair lift was working perfectly, and, indeed it has never been heavily used - just when my wife occasionally gets a knee pain - which will be more often with winter upon us. I have been told that two Bison 80 (12v) batteries are installed. 1. Is it possible to recharge the batteries with a 12v Car battery charger? ( In situ or removed from Lift). OR 2. Is there a simple procedure to reset the lift to take the charge - which seems more likely. I cannot afford the firms high fee - but your secret will be safe with me ! I would be happy to pay a reasonable amount for the service - we are not on benefit so cannot get any other assistance. Thanks.