Ethenol in our fuel!!!!
whoops wrong thread....
I switch batteries around constantly and am amused how many times you have to "attach" the battery terminals. How a 360 degree lead clamp on a lead post isn't making contact is just nutty but.... it happens. If you listen closely, you can hear the current arc just before it kills the connection. Jump out, wiggle the cable and you are off!
The only real fix is to buy good quality terminals and keep them clean. I don't know the science behind it but, I am guessing lead (or whatever they make them out of these days) oxidizes and only a small portion is transferring the current. This isn't the corrosive white crud either (lead sulfate?) just clean old cables and a battery that probably should have been retired twenty years ago.