The Lenovo 5B10W51900 is an internal rechargeable Li-Polymer battery for compatible Lenovo laptops. It fits inside the laptop as its battery pack, so it serves as a replacement for a compatible internal battery.
With a stated capacity of 52.5Wh, it supports everyday laptop use away from a mains outlet. The listed uses include office work, web browsing and multimedia playback; compatibility is limited to Lenovo laptops that support this battery variant.