blutker

I have a 98 jeep cherokee sport, 4.0, i recently have replaced the Crankshaft Positioning Sensor and it worked with a brand new bettery, but when i threw an old battery in there to check it, it was as if the sensor failed again. when i threw the brand new battery back in, it fried it again or for some reason isn't working. i did this all in about twenty minutes so i dont quite understand what would cause this issue. if there is any information on this topic it would be greatly appreciated. What might be causing the problem.