Lead-acid based chemistry
A lead-acid battery is normally at approximately 80% state of charge (SOC) when the bulk charge stage is completed.
The bulk stage duration Tbulk can be calculated as Tbulk = Ah / I, where I is the charge current (excluding any loads) and Ah is the depleted battery capacity below 80% SOC.
The absorption stage duration Tabs will vary depending on the depth of discharge; up to 8 hours of absorption may be required for a deeply discharged battery to reach 100% SOC.
For example, the time required to recharge a fully discharged Lead-acid based 100Ah battery with a 10A charger would be approximately:
Bulk stage duration, Tbulk = 100Ah x 80% / 10A = 8 hours
Absorption stage duration, Tabs = 8 hours
Total charge duration, Ttotal = Tbulk + Tabs = 8 + 8 = 16 hours