Battery dead?

Hi, I recently inherited a Compaq LTE 5380 laptop (old I know but it
does the job I want it for), when I got it, the battery was charged to
100%. Great, lasted the full charge time OK. When I go to charge it
now, it says "Battery 6%, Charging" - and doesn't move.

The 6% charge doesn't have enough to turn the laptop on for more than a
few seconds, then it's gone. I left the AC cord in overnight with the
laptop off, and it got to 12%. Switched the laptop on with just
battery, and it almost instantly went back down to 6%.

Anyone have any tips/info on how to bring this battery back from the
dead? I tried the Compaq battery calibration floppy, but it says the
battery is "full", when the lappy guage hasn't moved, re-plug the
battery in and it says "chargin"...."full" with the same outcome.

Is this battery toast, because it seemed to hold a good charge when I
got it?

--
A word of warning about matrices -- each column must have the same number of
elements in it. The world will end if you get this wrong.
-- eqn user manual