New ACC battery dead after <1 month under light load?

[pv]

I have a newly bought (11/2009) lead-acid battery that I got @ Schucks (or whatever their name is nowadays).
I installed the battery as a 12V accessory battery in my EV where it was unintentionally subjected to a light but prolonged (~3 weeks) load that dropped its voltage to 7V.
I removed the battery from the load and it has settled at 9V.
I have tried to recharge the battery w/ a standard 12V charger at 0.5A, but when I start the charge it immediately jumps to 16V and then creeps down to 10V in less than a few minutes.
From what little I know about lead-acid, I think I may have killed this new battery.
Does anyone else w/ more experience know if there is a way to revive the battery?
Am I suppose to gently wake it up w/ a low charge current, or am I supposed to jolt it back to life (defibrillate it) w/ a high charge current?

Pv