D.1 Valve regulated lead acid batteries

D.1.1 The minimum capacity of valve regulated lead acid batteries should be calculated in accordance with the following formula:

C min = 1.25(T1I1 + DI2 / 2)

Where:

Cmin

minimum capacity of the battery when new at the 20 h discharge rate and at 20 °C in ampere hours;

T1

total battery standby period in hours;

I1

total battery standby load in amperes;

I2

total battery alarm load in amperes; and

D

a derating factor.

D.1.2 Where Cmin /20 is equal to or greater than I2, it can be assumed that D = 1. When Cmin /20 is less than I2, the value of D should either be based on the battery manufacturer’s data or should be 1.75.

D.1.3 In practice, Cmin is unlikely to correspond exactly to an available battery capacity and therefore the next highest available capacity size should be used.

D.2 Batteries other than valve-regulated lead acid batteries

The minimum capacity of batteries, other than valve regulated lead acid batteries, should be determined by consultation with the battery manufacturer and should take into account the standby load, the alarm load, any required derating to take account of the higher current drawn in the alarm condition and a derating factor to take account of battery aging during the anticipated life of the battery.

Annex D (normative) Method for calculating standby battery capacity