How do you calculate battery charging current?

Here is the formula of charging time of a lead acid battery.

Charging time of battery = Battery Ah / Charging Current.

T = Ah / A.

Charging current for 120Ah Battery = 120 Ah x (10/100) = 12 Amperes.

Charging time for 120Ah battery = 120 / 13 = 9.23 Hrs.

Then 120 x (40 / 100) = 48 …..(120Ah x 40% of losses)