Problem with a Karelma Hercules Mobility Scooter.

Share your ideas about the practical side of caring.
I have been given a Karelma Hercules Mobility Scooter from the executer of a lady who had not used it for over a year and my intention is to get it going and offer it in exchange for a donation to the MS Society. As a result of it just standing the batteries are dead and I'm not willing to buy two new ones in case the machine is not worth renovating and my son lent me two used batteries which I have connected and connected to the trickle charger. I switched it on with the key, pressed the lit up information spots that said, "Key" "0%" and pressed the button under the dashboard upon which it emitted a noise like, "clunk". I pressed the handle to move the machine further but all I got was a, "Click" but it will not move. Any advice will be welcome.
From a Google search , it appears that Karelma are no longer trading.

Starting from scratch , I would try searching for :

1. Mobility scooter user groups

One on Facebook : https://www.facebook.com/groups/521416261204957/

2. Mobility scooter repairers ... local
3. Local garages ... not unknown for someone in that trade to know the answer.
4. Local carer / disability groups.

Once the problem is known , there are many advertisments for spares / manuals on the usual sites ... Ebay / EvilBay for one ... which all come with a " Health " warning if sourcing from anyone other than a official dealer.

Hopefully , another poster may be able to help with the technical problem.
No advice at all Brian ! But I did google 'Karelma Hercules' and got quite a few hits to the user manual :)