> Anyone want to offer an easy-to-follow, practical way to to
figure how
> much battery it will take to run lights, fans, etc. in the real
12v
> world?
> What would be helpful is a way to determine the amperage of
various
> appliances and then figure what the rule-of-thumb efficiencies
would be
> to then determine how many hours you could run various
combinations of
> things

Bosch has already done that. in their little Auto Handbook. this
is what i typed years ago on the list. it's available now at
www.type2.com, in the Library (technical articles) under Bosch
Terminal Designations ... this part is kinda waaaay down at the
bottom. :)
-----------------------------------------------------------------
----------------
and, while i'm at it, here's some interesting stuff:

 Power consumption of vehicle electrical leads (average values)

 Backup lamps                       25W
 Battery ignition                   20W
 Blower motor                       80W
 Cigarette lighter                 100W

 Fog lights                         35W each
 Fog warning lamp                   35W
     (red fog light on rear)
 Glow plugs                        100W each
 Headlamps, low beam                55W each

 Headlamps, high beam               60W each
 Heated rear window                120W
 Horns and fanfare horns            25W...40W each
 Instrument-panel lamps              2W each

 Interior lamp                       5W
 License-plate lamp                 10W
 Parking lamp                        3W...5W
 Radio                              10W...15W

 Side-marker lamps                   4W each
 Starting motor for truck          2.2kW...12kW
 Starting motor for car            0.8kW...3kW
 Stop lamps                         18W each

 Tail lamps                          5W each
 Turn-signal lamps                  21W each
 Vehicle heater                     20W...60W
 Windshield wiper                   90W