Quick Answer
Estimate Ni-MH charging time by dividing battery capacity in mAh by charger current in mA, then multiply by an efficiency factor, commonly about 1.2 to 1.5 depending on the charger and charge rate. For example, a 2000mAh cell charged at 500mA may require roughly five to six hours. Use temperature and negative-delta-V termination rather than relying on time alone.
Ni-MH battery charge time can be easily calculated with below method: battery capacity divides charge current, and then multiplies coefficient 1.2 or 1.1, time unit hour, e.g. Ni-MH battery capacity 1200mAh, charge current 600mA, charge time (1200mA/600mA)×1.2=2.4 hours, so that this battery need 2.4 hours with 600mA ni-mh battery charger.
Relationship between Ni-MH battery charge time and charge current is that charge time equals battery capacity divides charge current, considering charging consumption, so the calculated charge time needs to multiply coefficient 1.2 or 1.1. In common sense, you can calculate the approximate time. In addition, if it’s common charger with low charge current, the charge time will be very long.
When purchase charger, speed is not the first choose. It requests large current if charge time short, that will make battery heat greatly, which is bad for battery. 2300mAh Ni-MH battery, if charge current is 2300mA, your battery will be charged fully within one hour; and if booklet says it requires 23 hours to charge battery fully, the means the charge current of charger is 100mA, 2.3 hours is enough for fast charge with 1000mA charger, surely charge too soon is not benefit for battery itself.
