I don't know what other people do with their dead glider batteries but
I have been saving mine with the intention of eventually disposing of
them in a "green" way.

Turns out Checker Auto takes batteries for recycling. Not only do they
take full size car batteries but they also take any size SLA battery
and give a $3 store credit for each one, max 5 batteries per visit.
Split those 6+6+2 into the original 3 pieces for max return.

A box of garbage in my garage became worth $45.

Now to recycle those old brass radiators.

Andy