Now I enjoy all the benefits of battery operated power tools just as much as the next guy....They're convenient, flexible, and you can usually get quite an assortment of tools that run off the same battery. Then the inevitable happens....you get the dreaded blinking set of lights on your charger and the batteries die out almost instantly. Your faced with two options.....Drop $50-$100 on a new set of batteries or try rebuilding them yourself. Neither one of those two options appealed to me nor did I have the time to order the parts from overseas. As anyone in my situation might do, I scoured the internet for an alternative solution. I found guys connecting car batteries to their drill...ummmm no thanks. Then I came across the idea of using an old laptop power supply in place of the battery.....The voltage seemed right, but alas the wattage was too small. Even at 180 watts, the biggest pc power supplies couldn't provide enough to overcome the start-up current of my battery operated circular saw or angle grinder.
The principal of the pc power supply was sound, I just needed something bigger. After a little more research I found that the common everyday laptop power supply is what they call a "switch power supply". Turns out, switching power supplies are very common everywhere in the world, affordable and come in a variety of voltage and power ratings... I eventually chose a 350w AC/DC power supply produced by a reputable company called Meanwell with a voltage range of 15-18volts DC.
Wiring of the power supply to a dead battery is very straightforward, but the following instructable goes through the details step-by-step.