Quote:
How is it possible that two AA batteries which in series have a voltage of approximately 3VDC are able to fully charge a battery that operates at 5.2VDC?
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Can you clear up this point? TIA!
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Yes I can. The ETG has an internal voltage doubler circuit (possibly even a tripler, contingent upon the method they use to regulate the voltage). A doubler is not free. If the voltage output goes up, the current output will go down, but that doesn't matter if the cellphone or reader can still recharge. (It does matter in some situations if you want both higher voltage and high current.)
That's the advantage of the ETG: it needs only 2 AA batteries and it's smaller, lighter, easier to carry. You will see on the web some simple rechargers that use 4AA batteries, which will give you 6V in theory. Sometimes you get more than 6V because batteries aren't precision.
You have to be careful though. If the cellphone or reader expects to see 5V and you plug in 7 or 8V, it may or may not damage the device. That's why a regulator is needed: it forces the output to stay at 5V.
Now, back to the basic 4AA recharger. That may work with some devices, but as soon as the voltage falls below 5V, it will stop recharging.
It was due to all these considerations that I shopped for an emergency charger that was lightweight and regulated. If you measure the output of the ETG with a voltmeter, you will read a voltage that seems to vary between 4 and 6V in cycles. I think that's because it has a smart detection circuit that tries to figure out what voltage the device needs to recharge. For example, early Nokia phones needed 5V to recharge, but later ones need 5.2V. That 0.2V difference is important. Without 5.2V, Nokia won't recharge.
That's a lot of features to cram into a small recharger and maybe that's why they priced it so high to start. At those closeout prices, the ETGs are bargains, if you have some soldering skills.