Battery powered emergency phone chargers

[Stonent]

My wife works part time in the evenings at a local store as well as her full time elementary teacher job. She usually has about 30 to 45 minutes at most to get from job A to job B and doesn't always get a good charge on her phone in the car.

Sometimes her phone gets really close to dying while she's at job B.

I was googling battery powered phone chargers and looked at a few cheap ones on Aliexpress. One of which ran on a single AA battery and the others ran on 2.

Anyone used one? How well did it work?  The phone's battery is 3.8v or 3.6v I don't recall exactly. The phone is a Samsung Fascinate, a North American CDMA variant of the GT-i9000 Galaxy S. 1 or 2 AA batteries to me doesn't really seem like it would work well.  I would think at least 3 or 4 would be best. Or maybe a 9v rechargable NiMH battery with a really efficient 5v voltage regulator.

My idea for an ideal one would be something that could run in-line where she can leave it on the micro-usb cigarette lighter charger in her car and plug her phone in the other end. Then when getting out of her car, just unplug the input and toss it in her purse to keep charging.

What do you think?

[justanothercanuck]

my coworker has one for his iphone...  says he can charge it pretty quick, it's not enough for a full charge, but it's more than enough to turn off the low battery warning.  not sure what brand it is or anything, i could ask him the next time i see him. 

[Stonent]

I was poking around on youtube and found one guy who took apart an old laptop battery and pulled the Li-ion cells out and charged them with an external 3.7v Li-ion charger and used them in flashlights.

I happen to have one or more dead laptop batteries around here somewhere, the problem is charging the cells.

[Tuomas]

I started playing Ingress recently on my Android phone. Being an augmented reality game that uses graphics and GPS and that sends who-knows-what data through the 3G connection to Google, it drains the battery pretty fast.

I've seen alot of people playing using some sort of extra battery devices like that. here is one device I've seen, for example. Apparently they work quite well and seem to be almost essential for some people with old phones with old batteries. Doubling the battery life, or even better.

I actually just ordered some lithium polymer batteries from hobbyking and some parts from Mouser for trying to build my own only a matter of hours ago... Most of these extra batteries are meant to be charged through a microUSB port (so you can use the same charger you use for your phone), but I was thinking of also having two 4mm banana jacks onboard and a buck converter, so you could use a wide range of power supplies to charge it.

[andrea87]

Single cells out of any laptop battery pack are chargeable by any 18650 charger, usually found quite easily in the various chinese stores. i use one from dealextreme for my cree flashlights, and it works really well (not too fast charge, doesnt overvolt cells, ends at 4.2V spot on.)

You could pack two cells with some heat shrinking material, and add a small dc dc to dc converter to drop down the 7-8.5v the cells will give you to the normal 5V the cellphone uses. Perhaps, also add a balanced connector port for safer charging, like LiPO packs do have. Remember those cells dont like being shorted, and never discharge them below ~2.7V.

The whole thing being built would be quite small, 7x4x2cm for the battery pack, plus something for the converter.
A good, well made circuit could even fit in a 2x4cm board sitting on top of the batteries. Take a look at maxim / linear's ics, quite some good stuff there.

[jaqie]

why not just buy a second battery for the phone and an external battery charger for the battery?

[Stonent]

If I build a device, it's reusable.

[justanothercanuck]

why not just buy a second battery for the phone and an external battery charger for the battery?

having to swap batteries to charge them both is a pain...  an external battery pack can be recharged at leisure, even moreso if it's usb. 

[IanB]

Forget anything that uses a single AA battery, and forget about alkaline batteries. For this job you need either NiMH rechargeables or lithium ion rechargeables.

Have you looked at the Minty Boost? I have not tested one, but I trust Adafruit to deliver the goods.

[rr100]

The most efficient (albeit a little expensive but not a lot, we're talking $15-$30-$40) would be one of the "USB power packs" that has LiIon batteries inside (there a couple reviewed/mentioned on this forum, plenty more on internet or any online store, etc). Get something with at least 4-5Ah (usually calculated at 3.6V) and that should be the end of it.

On the other hand, if she isn't using the phone regularly "as a laptop" then something is fishy, probably the battery is acting up or there's some application that prevents "deep sleep". I know, smartphones are awful battery-wise but this one isn't a particularly bad one and should do one day without too much sweat, especially with a 30-45 min charge in between.