1985 Toyota Pickup starting problem

My toyota starts fine first thing in the morning. Then after it runs somewhere for awhile and shut it off it sometimes wont start on its own. It will start with a jump start or a kick start down a slope. And the after market gage shows its at 12v instead of 14v. Whats a good way to fix that, has to be the battery, alternator, or wiring. Please help me winter is here early (ALASKA) and I need it.