I have had no problems with lead acid, winter cold starting, since replacing the original cheap Banner battery with a Yuasa and the rectifier with an H-D Softail 74540-0. This charges even at idle at 14.2/14.3V which the original CE601 never did and the headlights don't dim as the revs drop any more either. I was also considering changing at some point to lithium and spoke to Ultrabatt. They recommended a pair of Ultrabatt UB-12400MM+ which come with a parallel link kit. They said they would work well with an H-D regulator but probably not with the original C-E regulator, where the charging voltage would be too low. The other thing Ultrabatt said was that you should use an external Lithium 12V charger conditioner every two months or so, to equalise cell voltages in the battery. If you get a CTEK one, this can also be left connected to a vehicle in storage.
Wilson
