Step 1: Opening the pack
Now remove the two groups of NiCD cells. They are 700mAh AA's, with little tabs holding them together. Each group is 3.6V, so the tool connect them in either series or parallel to select high or low speed.
Step 2: NiMH cells
Total price for all 6 cells from various stores:
http://www.batteryjunction.com/onepcsaa20ni.html 2300mAh, $10.80
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=222 2200mAh, $9.96
http://www.all-battery.com/index.asp?PageAction=VIEWPROD&ProdID=1336 2300mAh, $10.92
Step 3: Solder into packs
If your cells have short tabs like mine, you'll need to splice them together with a small piece of wire.
Once you have them connected in the right order, solder the tabs together and check the total voltage to make sure everything conducts.
After they're soldered, wrap some tape around each pack to hold them together and cut off the bottom tabs.
Step 4: Assemble and test the pack
Once you're sure everything works, snap the blue plastic part back in to close the battery pack. You should be able to charge it with the original charger, although it will take much longer because of the higher capacity cells.