Battery trouble

[dg463]

My ZR1 has been sitting for a while,and when i went to start it,the battery was weak, so i thougth lets give it a charge , but when i applied the terminals, it showed about 80 % charged on the charger screen readout, but then the charger went crazy, with the needle swinging wildly to the opposite side at the same time the charger started making a weird noise,needles to say i disconnected the he charger, and know battery id dead,any ideas, the battery is an Interstate.