Swap out your optical drive with a second battery to increase your unplugged power supply. The ThinkPad Advanced Ultrabay Battery II fits neatly into the Ultrabay media bay of select ThinkPad T61,T60 Series, Z61,Z60 Series, and R61,R60 Series notebooks and is compatible with the ThinkPad X6 UltraBase and ThinkPad X6 Tablet Ultrabase. Achieve all day computing (up to 8 hours or more) when you use the ThinkPad Advanced Ultrabay Battery II along with a high-capacity system battery like the optional ThinkPad Z60m/T60/R60 Series 9 Cell Li-Ion Battery, ThinkPad Z60t Series 7 Cell Li-Ion Battery, ThinkPad X60 Series 8 Cell Li-Ion Battery, or ThinkPad T61/R61 14W 9 Cell High Capacity Battery. Features & Benefits: - Operates and recharges in the Ultrabay media bay of select ThinkPad T61,T60 Series, Z61,Z60 Series, and R61,R60 Series notebooks or the ThinkPad X6 UltraBase and ThinkPad X6 Tablet Ultrabase. - Delivers the power of a second battery, but you do not have to carry around a spare loose battery. - Offers similar specifications to the standard system battery - Use it in the Ultrabay of the ThinkPad system along with your standard system battery to get up to twice the unplugged usage time as you could get with the standard system battery alone. Since the battery works in the Ultrabay you don't have to suspend the system to swap out the system battery to use the ThinkPad for an extended period of time.