I don't have a proper lead acid battery charger... But I own a small Yuasa 7Ah battery. I am using a 13volt 1.5A wall wart to charge it. And I have a volt-meter to check the voltage.
At what voltage should I take the battery off the charger?
See my stack exchange answer to "Lead Acid Battery Charger Design Factors" which relates, and follow the link there to the Battery University site which will tell you far more than you knew there was to know about lead acid (and other) batteries.
From the above answer note the quotes from the above website. Especially in this context
2.30 x 6 = 13.8V
2.45 x 6 = 14.7V
13.8V is the nominal voltage that many automobile systems operate at.
If you charge to only 12.6V as several people have recommended your battery will not ever be at full capacity and will have a shortened life.
And also Charging lead-acid batteries?