I have just re-celled a couple of the 18v batteries for a couple of my tools. One is a Ryobi one+ li-ion battery and the other a B&D ni-cad jobbie. I had read that the best way to get hold of the li-ion batteries was to buy an Aspire laptop replacement battery, break it open and use the batteries to make up the new pack. The batteries are 18650 type/size.
I bought an Acer AS09D70 4400mAh battery off Amazon UK for £11 odd + postage and broke it open. About an hours work and the new battery pack is now working fine. Double the capacity for about 1/3rd the price of a new pack.
The only requirements are that you know how to solder and ideally have a charger for li-ion batteries..
How did I find out that the Acer battery pack had the 18650s in it you may ask?? I found it on a 'Torch forum'. Yes! There are several of them
They discus all the ins and outs of that fascinating subject!