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?
Deep Cycle Batteries charge on 3 stages. Bulk charge, toping and float charge. During the bulk charge the current density Amper/ cm2 or Amper/dm2 it is very important. If the current is smaler than needed for the surface of electrodes the crystalin structure will occur. Sponge material is reversible, but cristaline material it is reversible and this is very important for PbSO4 too. After the battery gets charged 80% then the current decreased and during the floating is less than 1 Amper. The best choice is using a Smart Charger. The way a battery is used and maintained can change the battery life from 6 months to 7 years. Newer let a dischaged battery to rest uncharged, and discharging the battery at 50% before recharging can prolounge the battery life 2 to 3 times.