Hey all, neither of the batteries I have for my CMA4000 are good, both don't even charge at all, so I checked on ebay, I can get an official one for around $100 not including shipping, a knockoff one that looks like a good match is $40 without shipping or so, but I happen to have a generic laptop battery, lithium-ion, 11.1 volts, (6 cell) 4400mah, so I'd say almost double the life, though I've never had it run on battery to see how long it lasts.
Anyways I was thinking, maybe it is possible to hacksaw or whatever the cap of the SLA off, empty out the contents, gut the LI-ION and put it's cells inside, close it up and have a nice replacement battery.
Of course there is the issue of charging and protection, this is made for a laptop, but I am sure all that circuitry is inside, no clue what the charge input voltage is but I imaging 12v dc would work for it to charge up?
I think the biggest issue would be opening the SLA and cleaning it out without ruining it.