David,
Back when I'd just gotten my 3B, it was 6V. I didn't understand it. I had continuous problems starting it. I got in the habit of parking on an incline so if it didn't crank, I could coast and pop the clutch to start it.
Back then, converting to 12V seemed like the best idea to me. I've since learned that the size of the wires and clean connections are crucial. A weak/marginal charging system or battery can also ruin your day.
There is a special nut for the crank pulley that will accommodate a hand crank. There are videos online showing how to correctly hand crank (serious injury is possible if done wrong).