13.6v

This shows "SG lag" during a recharge. After a week on 13.6 you would think it would catch up. Nope. Note the "full charge" at about 2.65 per cell. That's 2.65 x 6 = 15.9v That is a little high, but there is no doubt that for 6s, you need to get well into the 15s. After SG is up, then you can drop to 13.6 for the Float and goose it every so often to destratify.

http://www.engineersedge.com/battery/specific_gravity_battery.htm