In the mid-1950's, we taped two 1.5V No.6 dry cells, (doorbell batteries) together, wired in parallel (+ to + ) on one line ( - to -) on the other. Dependable and durable 1.5V... NEVER seemed to run down unless shorted by accident, or by some idiot... Of course, we didn't fly every day except in Summer, and then at most two or three days a week.
Except for the Spitfire or OK type, I don't remember any commercial glow clips, so we used alligator clips - taking care not to short them, or "300 Ohm TV antenna lead" clips. They kept the polarity honest - a bit bulky, but certain - if the glow plug was good and the metal was at all clean.
In Brooklyn, NY, there were fewer family cars than today, few of us were of driving age (18+), and a family car was for other things, anyway. Over recent years I've mentioned some of our gypsy circus migrations by NYC Public Transit. A real trip, in many ways... usually including a healthy walking distance to "the actual field" with people, models and all field gear - and later - the weary, sunburnt return hike seemed much longer, the equipment heavier... It was all good, but better as memories than to reenact it nowadays...