The Mrs is having some mobility problems at the moment, so we've
dusted the power wheelchair out of storage. It's been stored for 8
years, with the batteries disconnected. They're the dry gel type. They
were put away after about 2 days use, so were effectively brand new.

Have reassembled chair, dropped batteries into holder and connected
up. Have plugged charger in, and currently it's just showing "on" -
none of the "charge lights" is showing. The charger is a super-duper
microprocessor controlled one (well that's what it says).

My gut instinct is we have 2 new paperweights on our hands. However I
thought I would seek the wisdom of crowds ...

I recall with old *car* batteries, that when they were completely
discharged, they wouldn't take charge either. My Dad used to connect
the dead battery in parallel with a charged one, with the charger
going to both, and that seemed to "catch" things. I'm guessing the
lower the charge, the higher the resistance until the charger just
can't work. Connecting another battery reduced the resistance, and
tricked the charger into working. I'm also guessing that being
"microprocessor controlled" this charger could work out such things by
itself, and deliver the appropriate charge as required ?