Recently we have noticed that some of our devices has been reporting strange fulgurations on their reported battery level. This is a graph over 24 hours:
When inspecting the problematic devices, their batteries are at full capacity and their average power usage is the same as a well-functioning device, however the power profile shows a intermittent tick every 2.25s on all the affected devices when this battery issue is present. This tick is not there all the time, it shows up at random intervals and power-cycling the device relieves the problems for a few hours but eventually the tick returns. You can see the power profiler when the tick begins here:
As a possibly related side-note, while trying to diagnose the issue I have seen that the `ble_radio_notification_init` event seems to be triggering at inappropriate times. I have attached a GPIO pin to go high/low in relation to the radio's state according to the event this function generates and you can see on the power profiler that the "radio on" event is triggered when data is written to flash.
After removing the usage of ble_radio_notification_init, the strange tick has disappeared and the battery levels are consistent.