I had a dead 1.5 Ah battery sitting around, so I decided to repackage it for more cells and higher capacity.

Printing: PETG is recommended for all parts

Print the bottom cap with supports going along the spine.

print the locking tab vertically with supports

Print the main case as shown I recommend tree supports for easy removal

the spring bar requires no supports and is preoriented

Pack Wiring:

Make sure you use quality 18650s that can handle large amounts of peak current I used Samsung INR18650s salvaged from other power tool batteries.

Assemble the cells together with 18650 holders: you will need to cut off the excess tabs on the holders in order for the pack to fit in the battery.

Reuse the old power connector from the old battery and connect it to the 18650 pack as follows:

The 2 thinnest black wires that are not shown in the diagram are used for the thermocouple; either connect a K-type thermocouple or simply bridge the 2 wires with a 10kΩ resistor.

With the electrical finished assemble the pack.
The locking bar slots into the battery case with space for the original spring from the salvaged battery.

place the spring bar in the slot after the installation of the spring and locking bar I recomend super glue to hold the bar in, but it is not needed.

slide the connector and pack assembly into the case, place the bottom cap on and use the 4 original screws from the salvage battery