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[pct-l] Re: Solar battery chargers

Steve Courtway wrote:

> guess I shoulda said JMT digital camera.

While I own a digital camera, I haven't tried hauling around a solar charger
for it.  The useful lifetime of a pair of NiMH batteries is sufficient for me
to shoot 36 photos (no flash), and I haven't taken it on trips longer than 3
days (combined cycling and day hiking; see
http://www.employees.org/~dsacer/touring/PinnaclesTour/index.html ) and so
haven't needed to charge the batteries while away from home.

However, there are several things worth considering here
1. What is the capacity (in amp hours) of the batteries?  
  NiCD and NiMH AA batteries generally have a capacity of something like
1200-1600 mAh, while a AA alkaline battery has a capacity of something like
3000 mAh, and the single-use AA lithium batteries, while expensive, have an
even higher capacity, not to mention lighter weight and more stable voltage
during discharge.

2. How long does it take to charge the batteries?
The off-the-shelf chargers I've seen are going to take the better part of a day
to charge a pair of batteries.  This means you'll want to carry two sets of
rechargable batteries.  In turn, this means that you'll need to take enough
pictures to discharge your batteries at least twice.

3. How resitant are the batteries to overcharging?
The solar chargers I've seen don't incoroporate the microprocessor-based smarts
that many of the better quality plug-in chargers use.  This means that they
will damage NiMH batteries, which are quite sensitive to overcharging. 
Depending on how long your trip is, this may or may not be an issue, but be
sure to experiment at home, and then take undamaged cells with you on your

4. What is your backup plan in case you have a cloudy day, and can't charge the
You'll want something here.  A set of lithium batteries will probably work
quite nicely.

5. Once you figure in weight and bulk of two sets of rechargable batteries,
plus a set of nonrechargable backup batteries, plus a charger, are you really
going to take that many pictures?

My guess is that rechargable batteries plus a solar charger don't make sense on
a trip where you plan on taking fewer than 150-200 pictures, and that you're
better off taking along an appropriate number of lithium batteries for anything
less than that. 

Also, be aware that rechargable batteries vary tremendously in their capacity,
even for batteries from the same manufacturer and using the same technology. 
Look at closely at their capacity before making a purchasing decision.

Do be aware of how temperature affects your batteries.  Different battery
technology behaves differently, but in general, too low or too high a
temperature will result in your getting less out of a charge than you would

Do be aware that discharging a rechargable battery too deeply can damage it.

Don't forget to bring enough storage to enable you to keep all those photos!