As I still use SLA batteries and am into that sort of thing, I designed and
built a charger/tester using a PIC microcontroller. It doesn't record graph
data as I didn't see the point, but it tops the battery up, discharges it
while monitoring the capacity, and charges it up again - or just charges it
if that is what I want. A 16 by 2 display shows what it is doing and
displays the capacity once the discharge phase is done.

If anyone wanted to copy it I would be happy to let them have the design
and software and help if needed.