FlyBuds 3 battery diagnosis and firmware telemetry

A left FlyBuds 3 earbud appeared to recharge almost immediately and then failed within minutes, while its right-side peer continued to run for hours. This project investigated whether the symptom came from a misleading percentage display, a charging fault, firmware behaviour, or a genuinely failing power source.

The work progressed from passive interface discovery and offline firmware analysis to an explicitly authorized, tightly gated bilateral firmware experiment. A 96-byte diagnostic extension exposed raw local battery voltage through an unused Bluetooth command without opening the earbuds.

Outcome

The isolated left earbud measured 3.98 V at rest, fell to 3.53 V after 98.963 seconds of audio, disappeared from Bluetooth by 105.069 seconds, and could not reconnect without charging. The stock percentage was following the same voltage collapse rather than causing it.

The leading diagnosis is extremely low usable cell capacity and/or high effective resistance in the cell or its power path. Abnormal PCB current remains possible because the sealed hardware did not expose calibrated current, delivered mAh, cycle count, state of health, or direct internal resistance.

Publications

• The complete investigation and measured battery collapse
• The reverse-engineering postmortem: 26 false starts and corrections
• The complete 70-sample voltage dataset

Publication boundary

The public record includes the reasoning, protocol model, diagnostic schema, measurements, limitations, artifact hashes, and the complete voltage dataset. It deliberately excludes proprietary firmware and APK binaries, personal identifiers, Bluetooth addresses, synthetic credentials, and a ready-to-run destructive flashing tool.

The diagnostic modification identified the failure; it did not repair the hardware.