Sony's WF-1000XM4 earbuds

Sony's WF-1000XM4 earbuds

Basic Information
Release Year	2021
Product Type	Earbuds
In Production	No
Official Website	https://electronics.sony.com/audio/headphones/truly-wireless-earbuds/p/wf1000m4-Black

The WF-1000XM4 are true wireless earbuds designed by Sony. They were launched on June 8, 2021.

Consumer impact summary

• User Safety – documented instances of earbuds overheating, swelling, & in some cases “popping open” during charging.
• Transparency – Sony has not issued a formal recall; guidance varies globally.
• Service Access – warranty and out-of-warranty support has been inconsistent by region.

Incident

Thousands of users, following firmware version 1.4.2 (released July 2022), have reported severe and uneven battery depletion, typically affecting one earbud. Most often the right. Symptoms include rapid discharge (for example, 1–45 minutes of playtime) and unusually high temperatures when charging.

Reported battery failures and overheating incidents

At least four documented cases involve earbuds physically swelling or splitting open with audible “pop” and chemical odor while charging in the case. One user reported an earbud splitting while being removed from the ear during a meeting. Additional cases were documented via community forums in mid-2023.

Underlying causes

Community posts & technical speculation point to a combination of:

• Firmware 1.4.2 disrupting charging controls and thermal management.
• Possible use of ZeniPower (Z55H) cells in early production batches (mid-2021 to mid-2022) being more susceptible to overheating.

Firmware v1.5 and v1.6.1 were released to mitigate the issue, but Sony stated only that these updates “reduce” battery loss rather than repair existing damage.

Sony's response

Sony's response varied by region:

• Japan – offered out-of-warranty replacements and pickup service for affected devices until September 2023.
• United States – some users received replacements beyond warranty; others were charged for repairs.
• European Union – some consumers received coverage under statutory protections; enforcement varied between member states.

Sony has not issued a formal recall or safety advisory, despite documented incidents. Official firmware notes refer only to “significant differences” in battery usage.

Consumer guidance

If one earbud shows significant battery drain relative to the other, or becomes unusually hot during charging:

• Stop using the earbuds immediately and contact Sony support.
• Report firmware version and charging symptoms.
• In some regions, free replacements have been provided even outside warranty.
• Avoid continued use if overheating occurs.

Documentation and evidence

Reliable source reporting includes:

• Large Reddit thread linking failures to firmware 1.4.2.
• Sony official community posts noting uneven battery drain and overheating.
• Independent blogs documenting battery swelling and explosions.
• Reviewer coverage advising warranty claims.