The formula to calculate the life of a battery in a given circuit is calculated by the formula: E.E=V.I.t The formula to calculate the life of a battery in a given circuit is calculated by the formula: E.E=V.I.t, using this formula, how can the time the battery will work be compared in different circuits?(please explain what this formula means).
 A: This formula says that the total electrical energy that can be delivered by a battery, $E.E$, is equal to some average power consumption, $P=VI$, multiplied by time $t$, which is a basic formula relating energy and power. The greater the average power consumption, the sooner the energy of a battery will be exhausted, the shorter the battery lifetime  
So, using this formula, we could determine the approximate lifetime of a battery in a circuit with the average power consumption $P$ as $t=\frac {E.E} P$.
In practice, batteries are commonly rated not by the amount of energy (Watt-hours), but by the amount of charge (Ampere-hours or Ah) they can deliver. So, for calculating battery lifetime, we would need to know its average current consumption, rather than its average power consumption, although, assuming some average voltage, one could be derived from the other.
The capacity of a battery is specified for certain conditions (temperature, discharge current level, etc.) and, as the conditions change, the capacity changes as well. So, in many cases, lifetime estimates of a battery are very crude. 
