The 6-cell Think Pad 81+ battery is compatible with T420s & T430s systems. These rechargeable batteries use Lithium-Ion & Lithium-Polymer technology to allow you to stay unplugged for longer. The battery lasts for 44 watt hours on average & can be recharged with the Think Pad External Battery Charger (40Y7625). The life of the battery differs due to many factors. These include: battery conditioning, power management, screen brightness, applications, features & other customer preferences.