This is Rafal from kontakt.io. Firstly, let me thank you for choosing us, it means a lot for us.
Propagation of battery level is not standard for iBeacons nor it is in any official iBeacon documentation, so that is why you cannot find the value using custom SDKs. Our iBeacons are propagating battery level in scan response packet which may be discovered using CoreBluetooth API in iOS. The level is one byte value at the 23rd byte in the packet.
Hope it helps :)
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