Change of CMOS battery in IBM Thinkpad 1400 2621
This battery is hidden under the keyboard slightly up and to the right of center of the keyboard. To get it out is a pain.
Start with the computer sitting flat, lid closed, lid latchs facing you.. just like you were getting ready to open and use it.
Spin it around, rear ports facing you. Right above the external video port, on the right hand side, there are two screws, at a diagonal UP from the port itself, very close to the bottom edge of the LCD. Remove them. There is a small notch between the screws, using a small flat-blade screwdriver, pry up in the notch and pop the platic backing free from the rear of the laptop. DO NOT open it more than a small crack, you are just popping loose a small plastic tab. Open it too wide and you will lock it closed again or break the plastics when you open the LCD lid.
Spin the machine around again, and open the LCD carefully as far back as it will go normally. Find the Power Button. The Power button is to the far right of a plastic 'strip, with 4 other buttons on the far left. There is a small clear plastic strip overlying this button 'tray'. Find the small notch in the bottom edge of the clear plastic strip, use the flat-bladed screwdriver, and gently pry up, popping the plastic strip out of the tab holes in the tray. Under this plastic strip is a black adhesive 'strip' that has a house, magnifying glass, etc. markings on it, and 'i Series' or somesuch printed on it.
Using a razor blade, peel up the black adhesive strip on the left and right ends of the button 'tray'. You will find two small silver screws. Remove these. Then using your screwdriver, or as I did, a dental pick, *gently* pry up the entire tray from the BACK edge of the tray, and by lifting up the left side of the plastic tray. You will have to work it out from under the edge of the LCD bottom on the left side. DON'T yank on it, there is a small cable attached to the bottom of it. You will be able to rotate it toward you and roll it over, exposing the small latch holding the cable in place. Its a small, press-fit latch like what holds a keyboard cable in place. You'll need to work it open by lifting the left and right edges till the latch becomes loose. Pull the cable straight out of the slot, remove the entire plastic 'tray', and set it aside.
On the far upper right of the keyboard there is a small metal tab holding the right upper edge of the keyboard. Reach around to the back of the computer, right-hand side rear, find the little square thumb-notch, and pull it out. The latch on the upper right edge of the keyboard should retract. Now, while lightly pressing down on the keyboard, push the keyboard away from you. It should slide backwards and the front tabs on the front keyboard edge will pop out of the slots. Lift up the touchpad area, popping up the bottom edge of the keyboard, clear of the plastics, then pull the keyboard slightly toward you. It should pop loose all the way around. DO NOT yank on it, there are 3 small cables attached underneath. You wil need to lift the keyboard up enough to reach the cables and pop the lockdown tabs loose, then pull the cables straight out of the slots they are in. The cable slots are attached to the motherboard, the cables are attached to the keyboard.
Removing the keyboard will expose a flat silver panel underneath. There are 5 screws holding down the panel, 4 in a 'box' configuration on the left, and a single one on the right, and several slide-tabs around the edges. Remove all 5 screws, then slide the whole tray to the right, while lifting up. The entire tray will pop up, with the video card heatsink attached on the left-underside of the tray. Set this aside. Directly in the middle of the big hole you now have is the battery. Its smaller than a standard desktop motherboard battery, looks like a small silver button. Gently pry up on the bottom-left edge of the battery, very carefully or you will break the plastic clips holding it in place, and pop it out.
All done. Reverese order to put it all back together.