How does one select the battery?
Battery selection depends upon the back up time required which in turn depends upon the frequency of power failure, average programme length and the presence of other back up source like a diesel generator set. One thing to remember is that the ampere hour ratings quoted by battery manufacturers are on a ten hour discharge basis and normally the back up time required will be much shorter; sufficient either to finish an almost complete job or to take a systematic shut down or to start the generator set. However, when the battery is discharged in a shorter time a derating factor has to be used which incidentally does not vary below 20 to 30 minutes. So approx half an one hour is a sensible back up time to select.
