Try to one time my battery died in my truck and a stranger stopped to give me a jump. she didn't know how so let me hook the jumper cables up, i forgot which to hook first, positive or negative, in a hurry and at the time didn't think it was a big deal i hooked both negatives up first then hooked the positives to the battery. after a minute my car started.. a month later i randomly ran into this person (we lived close by) she preceded to tell me that something happened to her car battery and it was my fault