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Description
Most likely you are using Bluez v5.48+ which no longer resolves/reports the GATT Battery service along with other GATT services so that TinyB library does not resolve it too:
https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.service.battery_service.xml
Temporary fix:
Downgrade Bluez to v5.47, instructions here.