Inquiry regarding the phenomenon where BLE TX power varies depending on the lithium-ion battery voltage

[sangyun.kim]

Device : wearable IOT device

Battery capacity : Max 4.2V (Typ. 3.7V)

BLE Tx Power : Tx power is highest when the battery capacity is 4.2V (measured in air, not conduction)

I wonder if this phenomenon is natural, and if so, what the reason is. 

[Ressa]

Hello,

How much variation are you seeing? Also which voltage supply mode are you using (DCDC or LDO mode) ?  Please note that the output power can vary in the range of  max +/-4 dB .