one thing about batteries is that their discharge characteristics are not linear. If a battery is rated at 12 Amp-hour, it will actually provide this capacity at 1/20 or 1/10 of 12 A (depends on manufacturer). So you get (say) 12/20 = 0.6 A for 20 hours.
Manufacturers refer to the A-h figure as the C-rating. The spec then applies for C/20 or C/10.
If you double this current, you get _less_than_ half the discharge time.
In general, high discharge rates (above C/20) will give a lower Amps x hours rating. Low discharge rates give a higher figure.
Regarding charging, I looked up some figures for Panasonic sealed lead-acid batteries. For cyclic operation, (fairly full charge then discharge) they recommend two charging methods:
Constant-Voltage: Use a supply of 14.6 to 15.0 V for a 12V battery. Initial current should be 0.4C or less. This is the quicker way.
Constant-Current: Limit the charging current to 0.1C from a higher voltage source. Charging time control is recommended to prevent overcharge.
Regards
Edwin Spector edwin.spector@att.com