Stay away from 8 volt batteries! I run a electrical shop, and this never works very well or for very long. First, if your starter is cranking too slowly, fix the problem. Second, to keep an 8 volt battery fully charged, your voltage regulator must be set at around 9.5 volts which will greatly reduce the generator and regulator life. If everything is right with your electrical system, your engine will start in any weather using 6 volts. Remember, there was a time when 6 volts was all there was. I hope this helps.
