Battery pack removal and installation - ThinkPad R400, T400
Use only the battery specified in the parts list for your computer. Any other battery could ignite or explode.
Removal steps of battery pack
Turn off the computer, or enter hibernation mode. Then disconnect the AC adapter and all cables from the computer. Note: If you are using a PC Card, the computer may not be able to enter hibernation mode. If this happens, turn off the computer.
Close the computer display, and turn the computer over.
Unlock the battery release lever (1). Holding the battery release lever in the unlocked position (2), remove the battery pack in the direction shown by arrow (3).
When installing: Install the battery pack along the slide rails of the slot. Then make sure that the battery release lever is in the locked position.