i have a lot of these TYPE of chargers, and they are cheap and fun, and interesting, but besides what was listed above, they are pure death to the internal li-ion/poly cell inside them WHEN you get ENOUGH full sun to charge them.
the black solar cells absorb heat like a solar oven (that happens with solar cells anyways, they get really hot), and that heat translates into the li-ion cell internally in the device.
like stated above, these items are (sorta more like) portable power units for pda and phone charging/running , wherin if you USE it as a solar item continually, the internal battery does not fare well.
so ya (sorta) end up charging them with the USB , then using them as the portable power they are, and in some dire emergency you might squeak out an hour of talk time, after torturing the unit in the sun for days. which could be extreemly usefull if say your grid went down, and magically no one elses did
anyways, take them with a grain of salt, they are still usable items for the price , but its really a portable power pack with a battery, and some minor solar for emergency.
also
some of the models of this style will REQUIRE a usb connect when the battery drops to low in voltage, the curcuit is to complex for me to understand, but it has a "logic" flaw that keeps the solar from retriggering the "protection" when low.
i am NOT trying to say anything bad about them, after all i was dumb enough to own MANY of them
, it just should be noted all the problems it can have.
i have redesigned a few to Shade the li-ion, instead of pulverise it, and it still has flukey issues like the above one.
they DO work, they are neeto as heck, many of them do use premium solar cells being the glass monocrystaline, they just have inherant design flaws that should be tended to.
generally as far as charging goes, you CAN get One phone 3/4 charged (about) after 2 days of full sun, and the curcuit used is not efficent as observed by the heat output by the curcuit during boost from the 3.6v to the ~5.0-5.5v outputs that are usually below about 500ma (running off the BATTERY inside). i got some that claimed a 500ma output they barely squeak out a 300ma, and some said 800ma and barely squeak out 500ma from the BATTERY.
the solar cells i tested, the small ones (about the size of a large cell phone) run about ~80ma in full sun, and the wider bigger one, that is about 3x5 really does have a 120ma output. did i say FULL sun
passive light landing on the cell might light up the charge light, but the quantity of charge is almost nullified by the leds own needs
so although some might CLAIM they will charge in your bright office, they dont tell of the month required to get a full charge.
on a side note, why are they making more and more BLACK electronics, with little processor heaters in them, with the battery as (almost) a heat sinc for the processor, they got no respect
