The iPhone 8 or later accepts up to 7.5W (5V/1.5A) to charge
its internal 3.8V battery. The battery mAh capacity (how many milliamps it can
supply for an hour) is
8 Plus 2691
XS Max 3174
In theory, if your phone uses around 200mA per hour, you divide the mAh capacity (think of a battery as a bucket of energy) by the energy use (mA) to give you the total usable time.
Using the bucket analogy, you can charge (pour in energy) as
fast as the bucket’s ‘mouth’ accepts it without spilling everywhere. Apple
limits the iPhone 8 or later to 7.5W (5V/1.5A). It does that for safety reasons
– 7.5W charging does not overstress the battery, but other brands are very
happy to fast charge at double or treble that wattage with no apparent issues.
Apple iPhone 8 or later support faster charging using an implementation
of the USB Power Delivery (USB-PD) standard that is a subset of Qualcomm quick
charge 4/+ and used by Samsung 15W, Huawei Turbo Charge, OPPO VOOC et al. USB-PD
is only for USB-C devices.
Apple supplies a 5V/1A (5W) charger in the box. It costs $29
as an accessory. This is clearly under capacity, and it’s disappointing that
such an expensive device has an inadequate charger. It also uses a USB-A to
Lightning proprietary connector cable.
This charger can take up to eight hours to go from 0-100% on
an iPhone XS Max – it is faster if the phone is switched off. It is unable to
keep up with the power draw for heavy users.
There are other Apple chargers that come as accessories or with various devices. The catch 22 is that these may require an expensive USB-C to Lightning cable which is currently $29 for 1 metre and $55 for two metres.
12W USB-A to Lightning 5V/2.4A – $29 (non-USB-PD
but delivers more wattage to charge faster)
18W USB-C power adaptor – $49 (also available in
the box with latest 11 and 12.9in iPad Pros)
30W USB-C power adaptor – $69 (also available
with MacBook and MacBook Air laptops)
61W USB-C power adaptor – $99 (also available
with 13in MacBook Pro laptops)
87W USB-C power adaptor – $119 (also available
with 15in MacBook Pro laptops) NOT TESTED
What effect do these have?
We discharged four Apple iPhone XS Max (supplied by Apple)
to 0% and started the charging process using the 5/18/30/61W adapters.
The results were surprising – well actually not to a techie,
but we will explain why later.
Back to the bucket analogy.
The 5W charger really struggles to fill the bucket faster
than the iPhone uses energy. If you use this charger make sure you switch off the
iPhone while charging.
With USB-PD standards, the battery charges in stages to
prevent overheating. Initially, it pushes up to 20V, then tapers down to lower
voltages and at about 80% tops up with 5V. The charger and phone have a circuit
to ensure delivery of just the right mix of volts/amps to avoid battery stress.
So due to the 5V/1.5A limit (7.5W), a 12W (not tested) or the 18W (tested) is all you need to achieve faster charging – a full battery in under two hours. Larger wattage chargers make no difference so don’t waste money on them if you are just using it on an iPhone!
Bring on full USB-PD – U stands for Universal!
The rest of the Android and PC world use USB Power delivery
In short, you can use any USB-PD compatible charger on any
USB-C PD compatible device. The larger the charger voltage and amperage, the
faster the battery will charge – within the pre-defined intelligent limits set
by the device and communicated by a handshake protocol between the device and
USB-PD delivers up to (maximum) 5V/3A, 9V/3A, 15V/4A and 20V/5A.