AA battery charger, emergency battery

[JumpinS]

Hi
has anyone ever tried out AA battery charger for O2 Exec, Qtek 9000,HTC Universal (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=260067712678) ?
I cannot imagine how this could possibly work with just one AA battery.

Same question for AA Battery Extender Charger (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=320041579760)

(If this has been asked/posted around, please point me to. I couldn't find it)

[linj]

I personally have a 2x AA charger I bought in Japan. Does mini-USB.

Um, I can't say for certain, but it did charge my Dopod 900 from 18% to 20%, at which point the thingie broke down and stopped charging and instead did a rapid discharge on my phone... bringing it down to 11% before I pulled it out.

It doesn't seem to charge unless the phone is off beforehand, as well, as noted in a Motorola-charger thread somewhere else.

I tested it with the alkaline batteries that were provided with it; your mileage might vary with rechargeable lithium-ions. I'm going to try 2x 2000mAh ones when I get back to Singapore and scrounge up a bit of change; I'll report back then.

[CWKJ]

One of the pictures seems to put the USB charger in the wrong place.

Is there a Universal with the charger at the SD Card area or is it at the side?

Full voltage (100%) is around 4.2V, so charging the Universal I expect higher voltage, isn't it not correct?

1 normal battery is usually 1.5V and rechargable type is 1.2V. Seems like need 4 batteries?

Is there a protection circuit for over charging?

[kecido]

Mmmm, perhaps I can help here.

Premise, I haven't test any of the chargers you mention (but they seem interesting to me).

I'm not 100% certain of this, but, I'm quite sure that there's no universal with the charge bay near the SD; this is just a simple graphic error surely made by the Ebay user that place the ad togheter, most PDAs have their power in around there!

CWKJ is absolutely right when He says that battery voltage is 4.2V, now, if you were going to charge the universal "directly" battery to battery (this is not the way rechargeable batteries are charged), you would need at least the same voltage that has the battery to be charged (this is 4.2V).
Battery chargers are "a little bit more complicated", each battery technology requires some kind of "different" battery charger (Acid like Lead batteries used in cars or UPSs, NiCd, NiMh, LiPoly, LiIon, etc.).
Some chargers verify the battery's voltage, others battery's current, others battery's temperature, others several of them, others a special mix of changes related to several of these parameters, and so forth.

The chargers you're talking about in this thread are contructed with a special switch mode power supply, the type that boosts (raises) the input voltage, they'll work as long as the "donor" battery has enough power (expressed in W or A*V). Also this power supply has a "efficiency" (expressed in %), so not all the energy is tranferred to the charging battery.
It depends on charger's quality how well will it work and how much will it last, the situation mentioned by linj seems like a defective charger to me.

One last thing, usually these boost converters have been made with over current and over protection circuits, and I'm saying usually, because one of my car chargers burnt itself out without any reasonable cause but a defective/poor design.
See the price that you're buying and you'll (not neccessarily) end with a good approach to the charger's quality.

[CWKJ]

With such cheap price, I would expect it to be direct to direct charging and not completed Switch Mode Power Supply charging.

[kecido]

For the first one mentioned by JumpinS (the cheapest), the converter seems to be present, there's a detailed photo where some components can be seen, including a little inductor that's absolutely necessary to make the converter.

The other one has no such photos but being expensivier...