Recharging a Lead Acid battery
Ouch.  My best guess is that your battery is toast.

Lead-Acid batteries suffer from several damaging chemical processes if they are allowed to remain discharged for long periods of time.  One of the real problems is something called "Sulfation".  You can use Google to search out that term and also look at the many attempts to build de-sulfation devices.  Wikipedia has a good description of the problem: Wikipedia

In general, I have good results with Lead-Acid batteries so long as they are kept charged.  We build our own chargers: Equalize voltage is 15.0Vdc and float voltage is 13.5Vdc.  The battery is charged with constant current until the current drops below the current limit value, then the charger drops into float mode.  There are better 3-stage chargers available now but we have had great success with those chargers - some of that gear is more than 20 years old and the users routinely get 5 to 7 years of battery life.