Emergency Chargers

Scribble

Member
Joined
Jan 21, 2010
Messages
387
Reaction score
6
Hi All- have any of you had any luck with those emergency cell phone chargers? The ones that are just a AA battery inside a tube with a USB port on it?

My company gave me one as a door prize at a conference recently, but it doesn't seem to do anything... The droid wakes up kind of when I plug it in, but no charging info displays.

I assume a AA battery is just too weak to charge it?

Or is it actually charging, just not enough to display the info?
 
Takes 850ma to charge the Droid IIRC....

AA's have 2700 (alkaline), 1100 (carbon–zinc), 3000 (LiFeS2), 1700–2900 (NiMH), 600–1000 (NiCd) mA
But I doubt enough to give more than a mild boost...
 
Last edited:
How does it charge by USB then? I thought max for USB draw was 500?
 
But USB is continuous....The AA just keeps going down.

Also I believe the Droid knows when it's charging off of USB.
 
A quick Wiki search says typical alkaline batteries have a capacity of about 1700 mAh to 3000 mAh while zinc carbon batteries range from 400-900 mAh.
 
The real problem is that a single AA battery only delivers 1.5v. USB is 5v. You can step the voltage up, but doing so will cost you amperage. I can't imagine that charger could provide much of a boost to the Droid at all.
 
The real problem is that a single AA battery only delivers 1.5v. USB is 5v. You can step the voltage up, but doing so will cost you amperage. I can't imagine that charger could provide much of a boost to the Droid at all.

Seemed to work fine for the various blackberries at the conference, but my poor droid couldn't get a quick fix. :(

(At least my friend's iphone was out of luck as well! :D)
 
Duracell PowerSource Mini

I picked up a Duracell PowerSource Mini, as a backup and emergency charger for my Droid:

  1. it provides 3Ah of capacity, enough to fully charge a Droid in 3-4 hours, if not enough time to get to a real power outlet.
  2. it comes with a car lighter 12V adapter: so you can run your Droid in a car too, while keeping the Mini charged.
  3. you can charge and run your Droid at the same time (i.e. via the USB connection), while keeping the Mini charged.
  4. fwiw: the mini-USB adapter isn't useful for the Droid, so just use the USB connector instead.
I got mine on-sale for $23, but you can find it for $30.
 
For one, the droid doesn't need 850mA to charge - 850mA just happens to be the max current on the motorola wall charger. USB spec is 500mA, and it charges fine off that. There is some minimum current needed, but I don't think any official number has ever been stated.

For two, the numbers somebody quoted on the AA batteries are Capacity, not available Current (measured in mAh, NOT current, which is just mA). The amount of current that can be drawn from a battery depends on the load, and the remaining capacity, among other things. It's not easy to estimate. You can't just convert from capacity to current - even if you were to divide by the number of hours a battery lasted, you'd have to insure that the current draw was constant for the entire period (which it won't be).

As for voltage - yes a AA is 1.5V and USB is 5V, but an emergency charger like that would just step the voltage up to 5V.

In short, I'm surprised that the charger didn't work. It is possible that it provides a voltage or current that is too low to charge with, but there's no way to assume that by the battery being used.
 
Back
Top