Charging Rates and Times
A standard overnight recharge is normally recommended for typical lead-acid batteries. This is based on a C/10 charge rate. (C=Ah capacity of your battery). For example. The recommended charge rate for a 7 Ah battery is 700 mA. Battery manufacturers publish maximum in rush rates for their batteries.
If a faster recharge time is required, the following formulas can be used to determine either the correct charge rate or the time required to recharge your battery to 90% of capacity. The Ah rating of the battery x 1.2 divided by the charging circuit max current, equals the amount of time (in hours) required to recharge the battery to 90%. These times are based on a fully discharged battery. For 100% recharging, add 3 hours "float" time to the charging time. If the battery is only partially discharged, the recharge time will be shorter.
Recharge Time (hours) =
1.2 x Battery Capacity (Ah)
|(add 3 hours for 100% charge)|
The rule of thumb is approximate however and battery data from the manufacturer is the best way to determine the maximum charge rate for a given battery. The 800 mA charger below has been "blessed" by the battery manufacturer for use with the 5 Ah and 7 Ah batteries on this page.