3.6 W(nominal) x 3.0 A = 10.8 WHr
10.8 X 60 X 60 = 38880 watt-seconds
38880 watt-seconds = 38880 joules
Of course your amp draw and low voltage cut-off will have some affect on this.
Battery capacity is defined solely on constant current discharge, not voltage, so that calculation doesn't really work for Lithium Ion batteries (where the voltage drops consistently as current is drawn and nominal voltage just means reference voltage). Fyi, the LG HG2 shows that the standard discharge rate is 0.2 C. So based on this, we can determine that at 600mA, the battery lasted 5 hours, which gives 3000 mAH as the battery capacity for that standard discharge rate.
Also, current draw and voltage cut-off can have pretty substantial effects on battery capacity. For example, the LG HE4 is rated for 2500mAH (also based on 0.2C, which means at 500mA it took 5 hours to drain the battery). However, at 3.2V cut off and 10A discharge rate, you'll get effectively about 1800 mAH. If you got to 15A, you'll get effectively about 1350 mAH. Throw in things like the number of cycles, constant vs intermittent discharge, changing current draw as voltage drops, etc. and it is probably impossible to predict how much energy one will get out of a battery while vaping.
It also really makes me appreciate how nice it is to have a Joules counter that I can use to evaluate my battery's performance on my SXM.
