Lenovo ThinkPad X240 Internal Battery (L13M4P21 / L13L4P21 OEM Replacement)

This battery is designed for Lenovo ThinkPad X240 series laptops. It is a slim internal lithium-polymer battery that forms part of Lenovo’s Power Bridge system, working together with an optional external battery for extended runtime. The most common part numbers are L13M4P21 and L13L4P21, which are used across X240, X250, and some X260 internal configurations depending on region and build.