On 9/3/2011 11:29 PM, David K wrote:

I thought all USB chargers were the same. They’re not. I plugged my TouchPad into a regular USB cord I had from some phone in the past and it gave a warning that the charge wasn’t strong enough. I also tried an iPad using a generic USB charger with thr iOS cable and got thr same message. I never realized that these things varied. What’s the deal? Is this just a tablet thing or what?  I have my phone plugged into the TP charger. No issues yet but should I be doing this? If we didn’t have these tablets I wouldn’t have this issue;)

Sent from my Windows Phone

Chris Leiter:

iphone ipod, phones, etc… 5W

iPad, Touchpad, Tab 10.1 etc… 10W

The iPad Charger and iPhone charger look identical aside from tiny 5pt font that says ’10W’ or ‘5W’

David K:

Interesting. I never knew. So any effect on plugging a phone in at 10w?

Doug Smith:

I plug my iphone into my ipad charger all the time. Mainly cause the kids have lost all the phone chargers! No damage yet…

Colby A:

I believe not. If its any similar to a power supply, that is just its "max" rating. But dont blame me if it breaks haha

David K:

Where the hell is the battery boss when we need him?;)

Doug Smith:

He is probably calculating his exposure from the tablet bet he placed earlier. Speaking of which, I need to change that to Jon don’t I?

You got enough article count DK. LOL


either way. i go by jon a lot more than i go by jonathan. google tends
not to listen to me when i change it. "no! your name is jonathan! i
have the birth certificate right here to prove it as i am google! your
all knowing overlord!"

David K:

Yup its Jon’s;)
And I Binged it. Guess what? No negative effects. If there were Apple would say it voids your warranty but instead they say it’s fine


Ahh, a Google guy with a touch of sarcasm. I like it. Leaves the door open to pull you from the dark side.

Well, pretty sure that all USB plugs/ports are a nominal 5V. Otherwise you would be seeing and smelling a lot of smoke.

Most phone chargers are in the 600mA to 1A range, or 3W to 5W (as in V x A=W). My wall charger is 1A, but my 2 USB Battery Backups are 500mA and 600mA respectively, and do a fine job of charging my phone, even while using it.

Should have no issues using a larger capacity charger, although some devices may refuse to charge with a lower capacity block.

Sent from my phone


My surround charger will not charge my atrix, doesn’t say if it is too much or too little energy.

Sent from my Motorola ATRIX™ 4G on the AT&T deathstar


The chargers should have power ratings on them. Compare them and you’ll likely get your answer :)

Sent from my iPad 2


Yup. The touchpad charger is rated at over 5V while all other chargers are at 5V tops.


Ok. Well my Surround charger is rated at 5V/1A, while my two USB mobile chargers are rated at 5.3V/500mA and 5V/600mA.  Most of my BT headphone chargers are rated at 5V/550mA.

So its got to do with the amperage rating. Guess they are worried that a charger with a lower rating will run hotter (at full load) although that’s unlikely to have any effect.  A device can be built to accept X amp load, so some will work and some won’t.

Remember reading in a blog that the LG chargers are only 600mA, but charge the phone just fine. Btw, the iPhone charger is rated 5V/1A, same as most HTC phones.


And this is why the iPad and other tablets don’t charge via USB when connected to the computer.  USB only puts out 5 when 10 is needed.

Doug Simmons:

Hey fellas, magic trick for you. I’m gonna blow your mind and demonstrate the power of MobilityLeaks pulling traffic even with such a sleeper of a thread like this. Not even gonna sex it up with girly pictures. It just feels like another win somehow. Even on a slow Sunday. What can I say, I got an eye for these things and I’m always reinventing myself.

In addition to being the Battery Boss, I am the ultimate blogger.

Also, glad to meet you Jon.


  1. 5V is pretty standard, 10V for some of the larger tablets.
    Current (A) is the big variance. You’d think that having an EE degree would mean I would know the impact of different current loads on batteries, but nay. I can confirm that WP7s do not like all of the variance, as one AC->USB block that I have has a different current load and messes with the internal software, making the phone still think it is charging, even after I’ve unplugged it. I use that charger at work, so I’m not sure of the output offhand, but I’ll take a look next time I’m in the office.

  2. So you are saying that an iPad uses a USB type charging plug (at the supply side) that requires 10V instead of 5V?

    In other words, can I plug my 5V phone into the 10V charging block plugged into the wall, via the universal USB connector? If so, that would be a very bad thing.

    I thought some devices won’t charge via computer USB, because the amperage rating is limited to something below 1A.

  3. jimski is dead on, (EE in the house) its all ohms law volts = current x resistance. Most USB charge devices are 5 volts so resistance changes between the devices to determine how much current is drawn. More amps rating equals better charger since it will charge anything requiring less amps at the rate determined by the resistance. That being said tables have larger batteries that require more amps to charge at a reasonable rate. The touchpad charger is rated for 2 amps and I use it for charging all my USB devices (nook, zune, iphone) I don’t think you would have an issue charging a tablet with a lower amp rated charger but it will definitely take longer.

  4. a lower power charger shouldn’t damage a phone, it will just be less effective. A higher power charger however, can damage your phone, if it wasn’t designed for it. Apple products are designed to be idiot proof, so any official charger should be fine, other manufacturers might suffer though.

  5. @kyuubi42:
    BS do you understand Ohms law? The only way you damage it is if the voltage doesn’t match but since it is a USB rated device the voltage is the same. Resistance is constant for the device especially the non-idiot proof devices. Even if you don’t understand Ohms law you should understand basic algebra volts = current x resistance. If volts is always 5v for a USB device and the resistance of the device is a constant then current = 5v / resistance ( constant for USB device). So do the math even if the charger is rated for 2 amps it doesn’t mean it is always delivering it, amps depends on resistance which is set by the device.

  6. yes I understand ohms law, I am an electrical engineer. I have also actually designed battery charging circuitry and have seen them blow up when too much voltage is applied, or the circuit allows the battery to try to sink too much current.

  7. I have a generic no name Charger with a USB output. When I plugged My Dell Streak charger cord into it, my Streak started flipping out,maybe even clicking internally, I immediatly unplugged it. I have used a “jawbone” Usb charger with the Streak with no problem. They are not all the same. Be careful. Peace

  8. More than likely the generic didn’t produce enough current for the streak and Dell didn’t allow for a lower current charger. I am no “battery circuit designer” but as a competent engineer I do not understand how the resistance isn’t fixed to pull the amount of current required. Any major manufacturer will compensate for that. Can’t speak for Chineese knockoffs though.

  9. what the hell are you talking about? Lower current doesn’t matter. USB charges at 100ma, 250 if the device then requests more power/ the data lines are shorted. The clicking sound is an inductor overloading, you’re hearing the insulation on the wires which comprise it breaking down.

    The Charing circuitry is designed and spec’d for an input at a certain voltage and current. depending on how lazy/cheap they’re trying to do it there might be no fuse, and the device might just keep on drawing current as long as the supply can keep giving it. If you exceed the design tolerances bad things can happen. End of story.

  10. I just assumed the wiring was not the same. Maybe + is on 2 instead of 3? And – was on 4 instead of the standard 1? That was my guess. It is a cheap charger prbably doesnt even have a ground. (Just talking out of my ass, I dont know) Just saying, I didn’t think it had anything to do with voltage. I am sure someone can find the answer. I am not cutting up my cords and chargers. Good luck. Peace

  11. Just to wanted to throw this out there. I plugged my iPad 2 into my MacBook Air just now for the first time. Guess what? It charges. I can plug the stupid thing into my USB 3.0, USB 2.0 and eSATA/USB combo port on my HP Envy 17 and it just syncs, no charging, but on the MacBook it charges… weird huh?

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