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.
This is great advice, and reminds me I need to check the mechanics work on the regulator that was installed just before I bought my 51 from my grandpa.
@ OP: My grandpa had put in an 8v years back when he said she " didn't like to start". When I got it, that's the first thing I did. Went to napa, they had a 6v for ~ 80.00. once I put in a properly sized bat cable (2/0), I was good to go. A 6v is all you need n
