Today we are going to do some applied physics and calculate the battery life of an e-cigarette. In order to do this, we need two pieces of information: battery capacity and stated voltage.
To make things easier, we are going to use the example of an e-cig box that has an 18650 battery (but what is actually in it?) with a capacity of 2000mAh, which is considered average for such a device.
The standard voltage for this kind of battery cell is 3.7V (or 4.2 when fully charged). This information allows us to shift from thinking about battery capacity to battery life, which is defined in Wh (watts-hour).
The equation is as follows: battery life (Wh) = battery capacity (Ah) X nominal voltage (V). Our example is thus 2 X 3.7, or 7.4 Wh. This means that the battery can produce 7.4W of power for one hour. However, the Wh is commutative, which means that the battery can also produce 14.8 W, double the power, but only for half an hour. Alternatively, the battery can produce 3.7 W during 2 hours … in any case, the total amount of energy doesn’t change, it is simply a question of usage rate.
How many pulls is that?
To convert Wh into number of vape pulls, we have to determine
- How much power is delivered
- The length of a pull
If a user vapes a 20W, for example, the battery will last about 22 minutes (1332 seconds). To calculate this, we have to divide the amount of power delivered (20W) by the battery power (7.4Wh) and then divide by 3600 (seconds, since we are talking about Watts-hour) to determine the result—in other words, 3600/(20/7.4). Afterwards, assuming that a single pulls last approximately 3 seconds, we can calculate a battery life of approximately 450 pulls.
To increase battery life, it is possible to multiply the batteries (in other words, the battery cells compiled in a set), either in a series or in parallel. Putting two batteries next to each other will double the capacity, while putting a battery one after the other will double the voltage. In both causes, the battery life in Wh will be the same because we are only increasing one of the two components.
Don’t forget to charge your batteries properly!