Real World emonTH Battery Life

The battery on my home emonTH Temperature & Humidity Node has just died for the second time in 14 months. Each set of batteries lasted exactly 221 days (7 months and 9 days)! The 2 x AA alkaline battery voltage started at 3.1V and the emonTH stopped working just after the voltage dropped below 1.2V (final dying breath was at a battery voltage of 0.8V!).  The two AA batteries installed were low cost alkaline batteries unbranded from e-spares. Battery life would not doubt be longer from some quality cells. 

I recommend using rechargeable alkaline batteries if possible in the emonTH, for least environmental impact. See my previous posts on emonTH battery selection and power consumption optimisation

My emonTH had a DHT22 temperature and humidity sensor connected and was set to the default post rate of one minute in-between samples. The unit was running V1.0 firmware (the firmware is now at V1.2, there have been a couple of minor battery life improvements). 

It's very impressive how the DC-DC boost converter onboard the emonTH continues to boost the depleting battery voltage to 3.3V, using this method allows the battery to be drained much further than powering the unit directly. 

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