The 6-cell ThinkPad battery 77+ is a replacement/spare battery for P50 system. The battery is rechargeable and can be used as replacement or as a convenient spare for mobile workstation ThinkPad P50 system. This battery is powered by Lithium-Ion technology and has a safeguard chip which authenticates with Lenovo systems. The battery lasts on average 90 watt hours and utilises over-discharge protection to ensure a secure flow of power.*Many factors affect battery life. These include: screen brightness, battery conditioning, features, applications, power management and other customer preferences.