The ThinkPad External Battery Charger gives you maximum power flexibility. You can recharge batteries for your Z Series ThinkPad notebooks without your ThinkPad system. Convenience and flexible operation are enhanced with charged batteries that are ready to go when you are.
Lenovo ThinkPad Z Series Notebooks
External unit frees up your ThinkPad notebook so you can continue to work off the system battery while charging a spare battery to increase your unplugged mobile computing time.