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estimating battery life

Posted: Sat Jan 19, 2019 11:16 pm
by noblerabbit

I am running esp32 on 2 AAA batteries (1000mAh).

I am able to measure average current during operation and deep sleep but I don't have insight when it comes to current spikes during startup and wifi.

Here is the sample scenario for which I want to estimate battery life.

My ESP32 device is in deep sleep (average current <10uA) for most of the time. Wakes up 40 times per day for 10 seconds (average current 120mA).

daily awake consumption: 40 * 10 seconds / 3600 * 120mA = 0.11h * 120 mA = 13.3 mAh
daily deep sleep consumption (24h - daily awake time): 23.88h * 10uA = 0.2388 mAh

Battery life estimation: 1000mAh/(13.3 mAh + 0.2388mAh) = ~73.8 days

I this a reasonable calculation? How big is the impact of startup and wifi current spikes on the battery? Where can I find this information?


Re: estimating battery life

Posted: Sun Jan 20, 2019 10:40 am
by loboris
You can easily test the battery life experimentally.

As the power consumption during deep sleep is minimal, just use the minimal sleep time (for example 10-100 ms) and see how long your system runs on battery. Multiply the measured battery life time with sleep time/run time ratio.
The actual battery life will be just slightly shorter.

Re: estimating battery life

Posted: Sun Jan 20, 2019 2:30 pm
by noblerabbit

Thanks for the fast reply.

That makes sense. Essentially I count the number of 10s wakeups before the battery goes dead and divide them by the number of expected wakeups per day (in my case 40) and I will get how many days the device should be operational.