Rebuild Your Ryobi ONE+ Battery Pack

I've had my Ryobi ONE+ system for over five years now and the batteries are shot. Let's see what it takes to rebuild one.

Screwdriver
Wire cutter
Soldering iron
Solder

Remove six screws from the bottom. Pull the black and orange sections apart.

Remove the cluster of batteries and identify the number and type of cells are contained in the pack. In this case, there are 15 Nickel Cadmium C cells.
From here we have some options. Since they're C cells, we can replace them with any popular battery chemistry.
We can use NiCad, NiMh or Lithium Ion.
NiCad or Nickel Cadmium are the least expensive and least powerful at $2.70 for each 2400 mAh cell. This gives us a material cost of $40.50 plus tax and shipping.
NiMh or Nickel Metal hydride is next up in cost and power. At $4.85 for each 5000 mAh cell. Replacement of the cells would be $72.75.
Finally, Lithium ion cells are $10.99 each for 3.6 volt 8500 mAh cells. Granted, you would only need 5 to get to the desired 18 volts, but then they're going to rattle around in the case.

With the cost of cells alone exceeding the cost of a replacement battery pack, I think it's time to pack this project up and go buy a battery pack.
Seriously, with brand new Ryobi NiCd packs available for as little as $30 and their new Lithium Ion pack for as little as $40, this is not a worthwhile project.
Don't forget to properly dispose of the old batteries.