The ThinkPad X200 UltraBase (43R8781) snaps easily onto your ThinkPad X200 Series and X201 Series ultraportable or tablet system for portable expansion. It features: Ultrabay Slim for device expansion for the following available options: ThinkPad Serial ATA Hard Drive Bay Adapter III Integrated second battery charger to charge a spare battery, all X200 Series or X200 Tablet Series batteries, by: Opening the access door on the X200 UltraBase