I have an old Montgomery Wards rider with an 18hp B&S engine that I only use for knocking weeds down a couple of times a year. When I went to start it the other day it would spin over but would not start and the negative battery cable got really hot. Then the battery got too low to spin it over so I hooked the jumper cables up to another battery and it started and ran fine. Why would the negative cable have gotten hot?