If you’ve ever let a car sit for a period of time and returned to find that the battery was mysteriously “dead”, you were probably experiencing a sulfate crystal build up. Often, people just buy a new battery and plop it in, but that isn’t absolutely necessary. [Kmpres] takes us through the process of building a desulfator. A desulfator works by putting high voltage pulses into the battery forcing the sulfate crystals to dissolve back into the electrolyte. From what [Kmpres] says, you can find “bad” batteries in all kinds of places, use the desulfator on them and have perfectly fine batteries when you’re done. You may recall doing something similar with a disposable camera.