The HTC Thunderbolt 4G Smartphone Replacement Li-ion Battery is a black rechargeable battery case with a capacity of 1500 mAh and a voltage of 3.7 mAh. It is designed specifically for the HTC Thunderbolt 4G model and is an OEM product from China. This replacement battery is perfect for those who need to extend the battery life of their HTC smartphone, ensuring longer usage and uninterrupted functionality.