I think you need to think laterally. I am sure some form
of current/voltage controlled circuit would be needed to charge from a car
battery or any other standard cells. Otherwise you could ruin your camera
battery.
I understand your concerns on a long trip, spare camera
batteries are nice, but usually expensive. I always carry one spare,
recharge battery in camera and make it the spare. Then both batteries kept
at full charge.
I had problems on a recent trip. First night out went to
do the daily recharge of the battery, found I had packed the charger for the old
camera. So investigated, and found I could improve battery life by turning
off the rear screen menu display. Only turned it on if adjustments
needed. Happily at a photographic convention found someone with the same
camera, he did a recharge for me, but I still went to the final week of travel
with 2 charged batteries, and no charger. Happily I easily lasted.
So IMPORTANTLY, check which camera functions drain the battery
and are not necessary all the time. Such as screen displays
operating continuously, or anti-shake. Turn off when not
needed.
To find oout more on batteries and how to look after them,
there was a website given on this list some time ago, the Battery University, http://www.batteryuniversity.com/index.htm
Worth a look at, and perhaps the original question could be
asked of them.
Enjoy your trip.
Jim Thyer
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