Stay unplugged longer with these genuine Lenovo batteries. These rechargeable batteries use Lithium-Ion technology and can be used as replacement for aging system batteries or as a convenient spare battery. The ThinkPad Battery 57+ (6 cell) features: - Lithium-ion technology - 6 cell system battery - Over-discharge protection to prolong the life of the battery - Battery energy (Watt-hours): 57Wh - Battery Safeguard chip authenticates with Lenovo systems