[pct-l] Bushnell Mini Solar

[Drew Smith]

Nominal battery capacity can be very misleading in terms of how many
times you can charge your iPhone.  In principle, a 6000 mAh battery
will give you 4 complete charges, as iPhones batteries have a capacity
of about 1500 mAh.

However, the phone will stop charging once the input voltage drops
below 5V.  Batteries do not output a constant voltage - they start
high, somewhat above their nominal value, and drop below that as the
battery discharges.  Both the battery type (alkaline, NiMH etc) and
the discharge circuit of your charger will affect the output voltage
profile.

So the key metric is not total mAh, but mAh above 5V in determining
how many charges you will get.  Example: my PowerFilm USB+2AA charger
has 2AA NiMH batteries with a nominal capacity of 2000 mAh each.  In
principle, I should be able to get at least 2 full charges of my
iPhone.  In practice, it is more like 40-50%. Since the unit has
sufficient solar panel area to do this 1-2 times a day, it meets my
needs.

Key points here:
1.  Test your charger out repeatedly before you head out on the trail
2.  If the results are disappointing, try "overcharging" it - letting
it continue to charge after the indicator says it is fully charged.
This will push up the output voltage just a bit, but enough to give
you significantly more output > 5V.

Drew Smith
Idyllwild - Walker Pass, starting Apr 8.