Gumboocho

Per my memory & fallible mind: Way back then they used generators, but not alternators. So you could run your car without a battery if you started it by rolling it down a hill. You could make starting easier when the existing battery would not crank the car, by hooking a 2nd 6 volt battery in series with the existing 6V (weak) battery, thus going up to 12 V (less internal resistance) briefly. So you could start the car with the 2 batteries in series, then hook back up just one 6 volt battery to drive away with. Even an automatic transmission car in those days could be started by rolling it down a hill or pushing it (they had real bumpers then) to 50 mph. With manual transmission, a much slower push should work. Thus the use of 12 V could be only for a few seconds, which didn't seem to hurt anything (but don't have the radio on). I had a friend whose standard procedure in jumping cars was to hook a 2nd battery in series just long enough to start the car. (Different topic: Now don't rebuild your engine in your driveway (like my friend did), then try to start it by pushing it, if that car is automatic transmission or say goodbye to your transmission, since the newly rebuild engine has too much friction & the transmission can't handle it in a push-start situation.)