# Estimating battery life from capacity and varying load

I'm having some troubles trying to estimate battery life.

I have a device that consumes 50mA under IDLE time, 650mA under transmission, and 100uA in Sleep mode.

I have a battery with 1.7Ah of capacity, the times are:

1. IDLE = 5s
2. Transmission = 10s
3. Sleep = 86,385s

I don't know how to calculate the average of the currents with the times of the various states, I need some help with this.

• During idle, the current consumption is 50mA x 5s. Similar formulas can be applied to the other two states... Think about your question a little more, alone. – Claudio Avi Chami Sep 2 '16 at 17:03

## 1 Answer

You should calculate the mean consumption which equals to :

MEAN CURRENT (in mA)= (5x50 + 10x650 + 0.1x86385) / (5+10+86385)

Now divide the capacity on the mean consumption to get the time (assuming you can drain all the juice out of your battery which is not so true.)

To be more accurate, you should examine the discharge curve (voltage as function of time) and examine where your circuit will actually stop to function. This may be the point where:

1. Regulator's dropout voltage violated. The output voltage will then start to drop.
2. Then the microcontroller / devices on your board will reach the non-operating-conditions (check your datasheet.)