We have had an issue with batteries draining much faster than expected on a few emonTH2 units, a few users have reported batteries failing after a few weeks or months.
We would expect ~4 years of battery life based on a 2600 mAh battery capacity and consumption of 0.055 mAh per hour (482 mAh/year), taking into account slightly earlier than full capacity drain cutoff as voltage falls below the boost converter minimum.
This is a relatively new issue following the switch to the LowPowerLabs library. I think the issue could have been the introduction of a wait until channel clear that’s part of the main release of this library, perhaps in noisier RF environments this has been keeping the emonTH on rather than letting it go straight back to sleep after taking and transmitting a reading. There were also some while loops without timeouts that could have caused a lock in the on state.
There’s now a new version of the emonTH2 firmware that removes this wait until the channel is clear and adds more timeout checks in the code. This uses the minimal RFM69_LPL library we’ve put together originally for the emonTx4.
The issue has been unfortunately difficult to replicate and so while I think there’s a good logical case that the changes in this update could fix the issue, it’s still a bit early to know if it has in practice and we will keep a close eye on reports of any further failures on units running this latest firmware.
This version v4.1.8 can be downloaded here:
GitHub - openenergymonitor/emonth2: emonTH V2 wireless temperature & humidity sensor with SI7021 sensor
It’s possible to upload this to an emonTH2 using a USB to UART converter, compiling the firmware either by using PlatformIO or by plugging the emonTH2 into an emonPi2 and using the firmware upload tool available from the Admin menu.
If you are affected by this issue and don’t have a programmer, you can also send the emonTH2 back to us and we can update the firmware for you. Please arrange this via our support email [email protected].