Using a battery spot welder and at least 0.15mm pure nickel strips, recreate the original structure of the pack. (And do a better job than me... although in my defence I did clean up and reweld some of the tabs after this photo was taken.)

Complete the underside first, then place it into the battery tub. Remember to take care with the tabs that come off the bottom and secure them with kapton or electrical tape before placing it into the tub.

Please only attempt this if you know what you're doing and have practiced. If you have even the slightest doubts please seek advice/help.

Once you have completed the welds, replace the circuit board and its paper, taking care to line up the thermistors with the holes in the cell holder.

Put fresh solder on the the pads on the board then solder the battery tabs down on their corresponding pads. It may help to hold the pads down with a small screwdriver (taking great care not to touch another pad), then once the solder cools enough to hold the tab, heating the screwdriver tip with the soldering iron enough to remove it).