Just a note you may want to apply dielectric grease on the ends of the garage door batterie(s).
I had a problem with corosive buildup a few flashlights (and a garage door opener) that I kept in my bike trunk . Probably due to the added moisture and vibrations.
Anyway nice write up, I am gonna do this but I am going to prolly use a lead from the power source instead (and hopefully not blow up my opener)
