Step 1: Removing the Cells and Charging
Measure the voltages and write them on the packs. Arrange the cells by voltage, less than .5, .5 to 3 and over 3.
I charge with cheap transformers I can find. This is very dangerous as you can over charge the cells. Never charge the cells past 4.2V.
If the cell is less than 3 volts you need to charge the cells at low current, less than 50mA. I use walkie talkies that usually charge 3 AAA batteries each. Charge until 3 volt and then switch to high current. After 3 volts you can charge up to 1A per cell. I use a 12 volt 4 amp charger and charge 3 cells on series.
Cell under .5 often have problems.
Step 2: Connecting the Cells
When you build a pack arrange the cells in parallel and series groups to get the amps and volts you need. Most laptop cells are 2200mAH and can be discharged safely up to 1C (2.2A for one hour).
For my pack I have 3 sets of 8 parallel cells in series. So my voltage is 12 to 9 and my max current is 17.6Amps. This works well for powering cheap car 12V motors. If you want more power you can add another series set and get 16 to 12 volts.
It is important that each series set has the same amount of parallel cells.
First tape your cells together in the parallel sets. Then tape the sets together alternating positive up positive down and tape it all together. I used small nails to connect the packs. Cut off the nail head, sand it and the top of the cells and solder the nail to the packs. I kept the 4 cells together from the packs. When soldering on the positive side it is super important not to get solder on the sides of the battery top. The outside of the battery is negative so the cell will short out.
I also soldered 2 14 gauge wires to the positive and negative sides of the battery. I taped the wires down so they couldn't be pulled of the battery.
Step 3: Battery Box and Padding
I rapped the battery in fabric and placed it in the box. I stuffed more fabric in the corners so the battery was secure.
The fabric helped with reducing shock and vibration but the battery can get too hot because its insulated.