The 6-cell ThinkPad battery 57+ is a replacement/spare battery for W541, W540, T440p, T540p, W540, L440 and L540 systems. The battery is rechargeable and can be used as replacement or as a convenient spare for several popular ThinkPad systems. This battery is powered by Lithium-Ion technology and has a safeguard chip which authenticates with Lenovo systems. The battery lasts on average 57 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.