That pic reminds me of when me and another guy were out riding the dresser bikes at night and at one of the stops his battery went dead. (no kick starter)
There was no one around to ask for jumper cables but I found a coat hangar, so I arranged the bikes so the batteries were both accessible and leaned them together so the handlebars touched.
The coat hangar was the positive, and the handle bars made the negative connection.
About 2 minutes of sitting like that with my bike running and his bike fired up.
