This is not a big design project as the other ones I have listed, but more of a feasible and cheap way to repair and improve the Canon High Power NiCad Pack. In my case the outcome is a High Power NiMH Pack with double the power of the original for less than half the price compared to what a new set of cells would have cost from Canon (work excluded).

Special Note: If You do something similar to what I have done I am in no way taking any responsibility of the possible consequences if something should go wrong. You may see this as a hint of what is possible to do if you can and know what you are doing, but you are the one that takes all the responsibilities.

My pack did not take charge very well and when I checked it it had around 10 V output compared to the 14.5 V it should have.

I took out the cells from the pack by:

1. Open the pack at the "plug" that attaches to the motor drive.
2. Unsoldering the two cables that corresponds to the pins (+ and -) in the plug where the charger is connected.
3. Removing all the gripping material from the pack, note that this is possible to do on bottom and also on front and rear (the later two I thought was just a pattern in the plastic the pack is made of, but it is removable and must be taken away).
4. Removing the cover on the left side by removing three screws, one on each of the sides bottom, front and back (on my pack they are blank metal screws).
5. It is now possible to get the cell pack out of the housing.

1. Get 12 cells of either NiCad or NiMH type in AA size with soldering tags and heat shrinkable tubes that the cells can be put into.
2. Solder the cells together two by two and secure them in a heat shrinkable cover. Note that the soldering tags should be bent so that it is close to the cells with the - end in the soldered connection (this in order to prevent any cell from being damaged by a shortage, this happened to me and is not a happy situation). Ensure during this process that the cell pairs are connected and shrank into a straight package without any angel on the middle (there will be very little room to get the final pack into the cover and a bent cell pair will be beyond the acceptable).
3. Make a good note on how the original cell package is structured and disassemble it in order to get your hands on the  "spacer".
4. Build a new package by using the cell pairs and putting them together according to the notes about the original package, glue with epoxy. It has to be noted that the NiMH cells are a little bit larger than the NiCad cells (0.1 mm in diameter) and that the heat shrinkable tubes available normally are a little bit thicker than the ones used by Canon. These two things may make it necessary to file the tubing around the cell pairs during the building process in order to make it possible to load the ready cell package into its housing. The final fit will probably be a little bit tight why it can be useful to have a string attached around the "spacer in order to simplify removal of the cell package during the work (and possibly even for future removal when the project is finished).
5. Cover all uncovered metal with a thin insulating coating, available at stores that sell electronic components.

If you have chosen NiMH cells you have to be careful not to charge them for more that 14 hours if using the standard Canon charger. NiMH cells are easily damaged if overcharged and the project was not that fun that you want to perform it too often.