According to the Battery Experts at Power-Sonic Battery Corp. recharge time depends on the depth of the preceding discharge and the output current of the charger.
To determine the approximate recharge time of a fully discharged battery, divide the battery’s capacity (amp. hrs) by the rated output of the charger current (amps) and multiply the resulting number of hours by a factor of 1.75 to compensate for the declining output current during charge.
If the amount of amp. hour discharged from the battery is known, use it instead of the battery’s capacity to make the calculation.
Battery capacity = 100ah.
Depth of discharge= 100%
Charge rate= 10 amps
100 / 10 x 1.75 = 17.5 hours