The Lenovo 5B10W51818 is an internal rechargeable battery for compatible laptops, intended for installation inside the notebook. Its four-cell lithium-polymer construction identifies the battery type for a replacement.
It has a stated energy capacity of 54.7 Wh, with listed voltage of 15.36 V and charge capacity of 3564 mAh. Check the exact notebook model before choosing a replacement.
Listed compatible examples are Lenovo ThinkPad X13 Gen 2 (20WK/20WL and 20XH/20XJ) and ThinkPad X13 Gen 3 (21BN/21BQ and 21CN/21CM).