The Think Pad battery 44+ uses advanced Lithium-Ion technology to create an efficient power source for the X230 & X220 systems. These are compatible with the X220 & X230 systems & are ideal to be used as a replacement or spare. The 6-cell batteries are rechargeable & allow you to stay unplugged for longer, lasting an average of 63 watt hours. However, they are not compatible with the Think Pad External Battery Charger (40Y7625). * Many factors cause battery life to differ. These include: power management, features, screen brightness, applications, battery conditioning & other customer preferences.