The 6 cell thinkpad 81 battery is compatible with t420s and t430s systems these rechargeable batteries use lithium ion and lithium polymer technology to allow you to stay unplugged for longer the battery lasts for 44 watt hours on average and can be recharged with the thinkpad external battery charger 40y7625 the life of the battery differs due to many factors these include battery conditioning power management screen brightness applications features and other customer preferences