Hi @Snara.2​ ,
The power consumption of a board depends upon the firmware that is running. This affects the current that flows from the rechargeable Lithium-ion battery (3.6V).
SensorTile.box firmware perform an estimation of the battery level (that is displayed in the STBLE app homepage), but doesn't.
Since you are planning to develop your own hardware, my suggestion is that you should monitor the consumption on the general Vdd line through a shunt resistor that can be connected to the microcontroller ADC, and that gives you a measure of the real time current consumption.
You might take inspiration from the STEVAL-MKI109V3 schematic, that is a bit complex but very precise (p.4), but probably a simple shunt resistor could be enough.
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-Eleon
