Battery for Apple Watch Series 4 40mm A2058 A2059

The Apple Watch Series 4 40mm Replacement Battery (Model A2058 / 224.9mAh) is a high-grade Lithium-ion replacement cell engineered to swap out worn, degraded, or swollen original batteries in the 40mm Apple Watch Series 4.  

Over time, daily charge cycles degrade battery health, leading to short usage times, watchOS performance throttling, or unexpected shutdowns during workout tracking. Installing this factory-spec replacement cell restores reliable battery performance and all-day power stability.  

Key Features

• Factory-Grade 224.9mAh Capacity: Built to match exact Series 4 specifications ($3.81\text{V}$, $0.858\text{Wh}$) for consistent and efficient power output.  

• Integrated Safety Protection: Built-in battery management IC prevents over-charging, short-circuiting, thermal overload, and voltage spikes.  

• Solves Battery Degradation: Fixes low battery maximum capacity alerts, rapid battery drops, or failure to charge on magnetic charging pucks.

Compatibility

• Apple Watch Series 4 – 40mm

  • Model Numbers: A1975 / A1977 / A2007 (GPS & Cellular variants)

• Battery Model Number: A2058

(Note: Not compatible with 44mm Series 4 models [which use A2059], or other Series 3/5/6/SE/7/8/9 models).

Technical Specifications

• Battery Model: A2058  

• Capacity: 224.9 mAh  

• Energy Output: 0.858 Wh  

• Nominal Voltage: 3.81 V

• Chemistry: Lithium-ion (Li-ion) / Polymer  

• Condition: Brand New

Note for Technicians: Replacing an Apple Watch Series 4 battery requires precision heating equipment to soften display seals, micro-spudgers to safely lift delicate flex ribbons, and replacement frame adhesive tape upon reassembly. Always perform 2–3 full charge and discharge cycles after installation to properly calibrate the new battery controller.