Instead let us dive into what makes up a battery pack. If you are like me, you have probably attempted to take apart an alkaline battery when you were a kid. When I took apart a 9volt, I was surprised to find several smaller batteries within. When I asked my father, he simple said, "How else do you think they get up to 9volts." Well the same is true for a rechargeable battery pack. A 14.4 or 18 volt battery, is built up of several smaller cells connected in series till the desired output voltage is created. As you can see from the picture, this battery pack is built up from what looks like a bunch of smaller "c" type batteries connected by little tabs, and covered with a small piece of cardboard. One can remove and replace each individual cell dead cell with fresh ones and voila, a new battery pack at a fraction of the the price.
Replacements cells can be sources from various Internet sites, or from your local batteries plus. http://www.batteriesplus.com/ However there is a tricky part to all this. From the factory the batteries are connected to each other via a spot welded tab. When you DIY, you will only be able to solder the connections back together, since most of us do not have a resistance spot welder. I also fear that welding a battery might have detrimental effects to its performance. Getting a good soldered connection on the smooth tabs of the battery is difficult. Scoring the surface is a must, but even that is not a guarantee for a solid connection. This is where ones soldering skills are put to the test.
Instead I opted to have my local Batteries Plus in Reno rebuild my De Walt 14.4V XR battery. It cost me $35 and was turned around in less than a week. They have two options, a lower mA rated battery build for ~$28 or the higher one I got for $35. Since my "XR" (eXtended run) pack was originally the higher output battery I opted for the same.
Taking apart the battery is a bit of a trick. Like the pictured battery, mine had a single screw holding the cover plate in place. However the edge was glued down and required some prying to free.
When selecting power tools we look at price, specs, performance rating and reviews. However most do not look at cost of replacement parts such as batteries. I have found that Ryobi tools have decent performance, but the replacement batteries only cost about $20. This has made the the Ryobi line of cordless power tool very popular. In fact I think that Ryobi subsidizes the cost of the batteries in order to sell more tools, just to capitalize on this fact. One would assume that their marketing strategy would be to slowy ramp up the cost of the batteries after the brand has gained popularity, but they have yet to do so.