This lithium ion rechargeable internal battery is specifically designed for the Watch Series 6 40mm. With a capacity of 265.9mAh and a voltage of 3.85V, it offers long-lasting and reliable power. If you're looking for an iWatch battery, especially a rechargeable one, or an internal battery, this lithium ion battery, namely the A2345 battery, is a perfect choice for your Watch Series 6 battery needs.