If you're willing to modify your battery box, this one will provide much greater cold cranking power than the stock 6V battery. It's the same one that's used in banks of 4 in older Diesel trucks to provide 24V for starting in cold weather. It won't fit through the hole in the floorboard, so you'll need to change it from underneath.

http://www.batteriesplus.com/product_search/23931-Ultra-Pro-Series-Fleet,-Heavy-Duty-Group-4-Hi-Capacity-6--Volt-Battery-SLI4A.aspx

(The link won't reproduce correctly- - - -do a copy/paste into your browser line at the top of the page!)

Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!