A USB Battery Charging port can deliver 1.5 A of current at 5 V. My iPhone 8 for instance came with a 1 A charger, so I can't assume that it'll use more than that from a USB A socket (it can however use USB Power Delivery with a USB C cable).

Do any iPhones take advantage of the higher current from a USB Battery Charging port?

Wikipedia has this to say about USB Battery Charging:

The charging device identifies a charging port by non-data signaling on the D+ and D− terminals. A dedicated charging port places a resistance not exceeding 200 Ω across the D+ and D− terminals.

Per the base specification, any device attached to a standard downstream port (SDP) must initially be a low-power device, with high-power mode contingent on later USB configuration by the host. Charging ports, however, can immediately supply between 0.5 and 1.5 A of current. The charging port must not apply current limiting below 0.5 A, and must not shut down below 1.5 A or before the voltage drops to 2 V.


So, if a device draws more than 1.5 A of current from a USB A port then — to me — that suggests that the device is not in spec with regards to USB Battery Charging which, according to the above quote, can deliver a maximum of 1.5 A. My conclusion would be that in that particular instance the device is using some other scheme of determining how much current to draw. That doesn't preclude the existence of support for BC as well, naturally.

I took an interest in USB charging recently while repairing a USB A power bank, and started wondering whether this BC standard is actually being used by devices. Since I have an iPhone I thought it would be a good candidate to ask about.

While I get the impression that my phone does take advantage of higher current, it is purely anecdotal and that also doesn't preclude the possibility that it's using some proprietary method.

1 Answer 1


Do any iPhones take advantage of the higher current from a USB Battery Charging port?

Yes. I know from my own personal experience (using a USB meter) that the iPhone 7 plus draws up to 2.1A at 5V. I never had the chance to test it, but I do remember the iPhone 6 would “complain” that it would charge slowly if I used a charger with less than 1.5A capacity.

Apple has an iPhone comparison tool that will allow you to obtain the Tech Specs for models from the iPhone SE (1st gen) to the latest model. From what I can tell, all iPhones starting with the iPhone 8 support fast charging meaning it takes advantage of the higher current rates.

so I can't assume that it'll use more than that from a USB A socket

Your phone will only draw what it’s capable of drawing and the adapter is capable of delivering. If only 1A is available from the USB adapter that’s all the phone will draw. Higher amp adapters will have the data pins shorted with the 200ohm resistor to “tell” the device that higher wattage is available.

Newer USB-C chargers that conform to the PD spec (power delivery specification) will negotiate the charge rate with the device. They will require USB-C adapters of at least 18W (18 / 5V = 3.6A)

  • As I understand it Battery Charging ports don't need any negotiation, but when you say "all iPhones starting with the iPhone 8 support fast charging" that actually refers to Power Delivery which requires negotiation, and USB C in order to ensure proper cabling. Also, an iPhone 7 drawing 2.1 A from an USB A socket, isn't that out of spec even for Battery Charging's 1.5 A? If so, then it must not take advantage of Battery Charging, but use some custom Apple-specific way to detect the availability of 2.1 A? Or did I misunderstand something?
    – Andreas
    Commented Jan 7, 2023 at 3:47
  • It would be interesting to know if iPhone 7 - 8 was a cutoff point where iPhones started solely relying on the standardized USB power detection / features.
    – Andreas
    Commented Jan 7, 2023 at 3:51
  • It was the implementation of USB-C PD when the iPhone 8 was released that they implemented it. As for “regular” USB charging, if the phone was capable of higher charging rates, it would “look” for the correct voltage on the data lines. If it was there, it would draw more current
    – Allan
    Commented Jan 7, 2023 at 4:06
  • I find it rather difficult to follow. Are you talking about USB Battery Charging? Because I've only ever come across that it communicates with resistance values (see wiki quote) — never voltages.
    – Andreas
    Commented Jan 7, 2023 at 7:06
  • @Andreas, the adapter and [multimeters for that matter] don’t look for resistance values. It looks for a certain voltage level that’s a results of said resistors. .
    – Allan
    Commented Jan 7, 2023 at 7:14

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