Place the new battery in place and align the far contact with the outer solder pad. Use a small strip of electrical tape to hold the cable against the solder pads.

Installing the battery upside down (with the cable facing up) will destroy the logic board.

Place the strip of tape over the end of the battery ribbon cable to cover two of the solder pads and hold the contacts down against the logic board.

Heat the rightmost contact until the solder below melts, then apply a small amount of solder to the contact, allowing it to flow through the two holes in the cable and down to the logic board.

Do not apply too much solder. The amount required for a proper bond is miniscule.

As soon as the solder has flowed into the joint, remove both the solder and the iron.