Batteries are usually connected in Series as in Series
Voltage get added up and current remains the same.

**BATTERY RATING CALCULATION**

The formula employed
rating calculation is as stipulated below:-

**FORMULA EMPLOYED:**

Capacity of Battery (AH) = (DC Current X Duration in Hrs)/(
%age capacity utilization)

Where, DC Current = (UPS (KVA) x 1000 x Load Power Factor
(=1))/( Inverter efficiency x End Voltage)

Hence, VAH = AH x
Nominal Voltage

For e.g.: for 3 KVA
UPS, 1 hour Backup having 18 no. batteries:

DC Current = (5 x 1000 x 1)/ (0.95 x 10.5 x 18) =27.85A

Battery “AH” = (27.85 x 1.0)/ (0.62) = 44.91

Hence , 18 no.s of 12V/42AH batteries will suffice .

TOTAL VAH = 18 x 12 x 42 = 9072 VAH

The following assumptions have been made in the above
calculations:-

1. DC Voltage – 216 for 5 KVA

2. End cell voltage / battery of 10.5 V

3. Load Power Factor = 1.0

4. Inverter efficiency = 95%

% Capacity utilization is:

Duration % Capacity utilization

½ hr (30 min’s) à52%

1hrs à
62%

2hrs à74%

3hrs à83%

4hrs à85%- The
*amp-hour*is a unit of battery energy capacity, equal to the amount of continuous current multiplied by the discharge time, that a battery can supply before exhausting its internal store of chemical energy. - An amp-hour battery rating is only an approximation of the battery's charge capacity, and should be trusted only at the current level or time specified by the manufacturer. Such a rating cannot be extrapolated for very high currents or very long times with any accuracy.
- Discharged batteries lose voltage and increase in resistance. The best check for a dead battery is a voltage test under load.