452e0d97_HAL_0_5_14_Specification__Description
[Key (type)] battery.charge_level.unit (string) [Values] Examples: mWh, percent [Mandatory] No [Description] 
The physical unit used by the charge level properties (maximum and current). In many cases, this property is omitted - which indicates that the charge properties are measured in some unknown units. The units should never be mAh as this is not a measurement of charge.
HAL 0.5.14 Specification
Description