ThinkPad A Series or T Series customers with extended unplugged power needs will want to consider keeping an extra battery in the Ultrabay 2000. The ThinkPad Ultrabay 2000 Li-Ion Battery is a rechargeable battery, which can be used in the Ultrabay 2000 of the ThinkPad A Series or T Series. Adding this battery to your system maximizes your unplugged usage time. This battery has nine cells providing an output of 10.8 V and can be recharged in two to five hours depending on the Thinkpad system usage.