Calculate Battery Back-up
To calculate the battery back-up one should know the AH (Ampere Hour) rating of the battery. Incase of mobiles it is MAH i.e. Milli Ampere Hour. Usually this rating is mentioned on the nameplate of the battery. "Ampere hour" rating means that battery can supply the power to the load at the mentioned ampere hour rating for one hour continously. Let the "AH" rating of the particular battery is 20. Then, if the load connected to the battery is 20 amperes then battery back is 1 hour. If the load connected to the same battery is 5 Amperes then the battery back-up is 4 hour. Formula : Battery Back-up = X/Y hours where X= Ampere Hour rating of battery Y= Load current in "Amperes"