batteryLevel property

@override int? get batteryLevel

An estimate of the battery level of the eSense device.

It assumes a linear relationship based on a regression on these measures of battery and voltage levels:

  B  |  V
 ----+------
 1.0	| 4.1
 0.8	| 3.9
 0.6	| 3.8
 0.4	| 3.7
 0.2	| 3.4
 0.0  | 3.1

which gives; B = 1.19V - 3.91.

See e.g. https://en.wikipedia.org/wiki/State_of_charge#Voltage_method

Implementation

@override
int? get batteryLevel => (_voltageLevel != null)
    ? ((1.19 * _voltageLevel! - 3.91) * 100).toInt()
    : null;