# calculating battery life with intermittant load

I’ve got a circuit that draws 15ma when powered on, and draws no current when off. If it’s only active for 5 seconds every 5 minutes, how long will it last if I have a battery pack with a 2000mAh capacity?

I've got a circuit that draws 15ma when powered on, and draws no current when off. If it's only active for 5 seconds every 5 minutes, how long will it last if I have a battery pack with a 2000mAh capacity?

2000mAH = 133.3 hours at continuous load.
Duty cycle is 5/300, so 300/5 = 60 * 133.3 = 8000 hours

Does it really draw ZERO when off? The off-time load is 59X more important than the on-time load.

Two more things:

1. The battery has a self-discharge rate. You should include this.
2. Something makes the circuit wake up every 5 minutes. What is this "something"? Does that draw any current? If so, include that!

Oh and if the battery pack is nominally 2000mAh, don't expect it to have that capacity for very long, most chemistries lose a good fraction of their capacity over their useful lifetime. Call it 1200mAh or something like that to get a conservative estimate.