I've never heard of a 29V battery. 24V maybe.
In either case, why on Earth would you expect to charge it up to 100V?
Can one respectfully suggest you find a local technician and ask him to look at the chair? I strongly suspect you don't really have a clue - and that's not a comment inspired by your age.
All he needs to do is understand simple batteries and chargers and have a bit of nonce when it comes to the mechanicals.
You could also try contacting Sherbourne