iPhone stops charging if battery too low

Question

MJ2008 Author

Level 1

8 points

iPhone stops charging if battery too low

Most of the time, my iPhone sits in the 3G dock and charges and syncs and is happy. The "lightning" icon in the battery shows it is charging, and when full it goes to the "power plug". But if the battery gets too low, less than 10% charge, then it will connect and start charging, but after a minute or two it stops and there is no icon (lightning or plug) just a battery indicator (on phone and iTunes). This has happened a few times, and I've now worked out the occasions, and my theory is that the phone is going into a power-save mode to retain more power, and thereby shutting down the charging mechanism too. To get it to work again, I have to put it into another computers charger, let it charge to 50% or so, and then it will work fine in my dock.

I'd welcome hearing if anyone else has had this, and any solutions.

(For technical info, this is Windows XP Pro, latest iTunes and iPhone software, direct USB connection, rebooting the PC doesn't fix it.)

PC, Windows XP Pro

Posted on Nov 7, 2008 7:09 AM

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Answer 1

Macaby

Level 3

923 points

Nov 9, 2008 9:07 PM in response to MJ2008

The answer as above is "Don't let the battery get too low". If you do, figure that you will have to charge for a while before you can use the phone again. Yesterday it happened to me while in my car. I have a car charger that does a pretty good job, but it was useless until I charged for several minutes. Must be something to do with the battery.

I have a Nuvi GPS that does the same thing if the battery gets too low. The first time it happened I thought was "toast". However, after charging for a couple of hours it finally booted back up.

My rule is if I get the "Low Battery Dismiss" warning, the IP either goes on a cord or is turned off until a charger is available.

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Answer 2

MJ2008 Author

Level 1

8 points

Nov 10, 2008 1:16 AM in response to Macaby

To be clear, this is not about the device not operating at this point due to low battery, it is about it not charging. If I just leave it alone for an hour, it loses more charge, even though it is on the dock. If it was completely flat, that would be very different.

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Answer 3

Nov 10, 2008 6:03 AM in response to MJ2008

It's likely that the USB port on your computer cannot supply the 1 amp that the phone needs for its fast charge rate. Or you are using a hub, or you have other USB devices connected that also require power and there isn't enough left for the phone. As a simple test connect the phone to a mains charger when this happens. If it starts to charge then the problem is that the port on your computer cannot supply the required current.

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Answer 4

MJ2008 Author

Level 1

8 points

Nov 10, 2008 6:33 AM in response to Lawrence Finch

That is possible, but why would it work when I have a 50% discharged battery, able to take it to 100%, but not charge it up from 90% discharged? Maybe it can't do fast charge, but why not slow charge it instead?

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Answer 5

icebike

Level 3

740 points

Nov 10, 2008 6:26 PM in response to Lawrence Finch

Nah, that's not it, all that would affect is the rate of charge.

The specification for a computer usb port is half a watt. The wall charger puts out one full watt.

Still the voltage should be the same, and it should be able to charge, just more slowly.

If the USB port is not giving a full 5 volts (in addition to giving only only half a watt) there could be problems charging, depending on the charge circuitry in the phone. (If they left out the voltage controller on the expectation of always having a a full 5 volts, a slightly low volt reading on the USB port could prevent topping off completely).

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Answer 6

ianmcp

Level 1

5 points

Nov 9, 2008 1:45 PM in response to MJ2008

same happens to me. if the battery is too low it will only pick up from a mains charger. once it's high enough it will charge n sync, otherwise it just sync n drain ! 😟

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Answer 7

icebike

Level 3

740 points

Nov 9, 2008 6:39 PM in response to MJ2008

Patience.

Give it an hour or two, not a minute or two.

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Answer 8

Nov 10, 2008 8:48 AM in response to MJ2008

It's just physics. A battery at a low state of charge (lower voltage) requires more current than one at a higher state of charge.

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