Now that EU is doing yet another round on Common charger for mobile radio equipment2019/2983(RSP), it inspired me to take a closer look on USB-C or USB 3.1 cables.
I got me a couple of cables:
One USB-C cable is for micro-USB and another is for Apple's Lightning connector. More details about the Apple-cable can be found from support article About the Apple USB-C to Lightning Cable. They claim, that some iPads/iPhones would go up to 96W on a compatible charger. Qualcomm Quick Charge @ Wikipedia has more details on that.
Exibel 38-9107 (18W), note: Exibel is a Clas Ohlson -brand
A generic Huawei USB2.0 (10W)
To get a real slow rate of charging, an ancient 2.5W USB-charger could also be measured. As an impatient person, I don't think I own such a device anymore, so I couldn't measure it's slowness.
Then I took my iPhone 8:
It wasn't completely drained. The thing with Li-Ion charging is to avoid the battery heating. Given the chemical reaction in a Li-Ion cell on charging, it is not possible to pump too much current to a cell while maintaining efficiency both on energy and time. A typical charging cycle follows a very careful formula charging the cell more when it's drained and less when it's reaching full capacity.
My testing was around 20% capacity. Here are the measurements:
Note: Obviously my measurements are from the wall socket. Not all the energy goes to the iPhone, as there will be some loss on the charger itself.
Huawei 10W charger measured 9W, which is nice!
Exibel 18W charger measured 14W, which is ~20% less than expected
Celly 30W charger measured 18W, which is ~40 less than expected
An iPhone 8 won't be using the Apple-mentioned 96W, no matter what. The measured 18W is a lot more than USB2.0 can do, meaning the actual charging will be LOT faster on an near-empty battery. Note: it is not possible drain Li-Ion cell completely, your phone will shut down before that happens. If I'm happy to get 80% capacity to my iPhone, charging for that will happen in half the time I can get with a regular 10W charger. During charging, as the capacity increases, the rate of charging will decline, a lot. For the remaining 20% I won't benefit from USB-C charger.
iPhone 8 won't sync data via USB-C. That's really weird. For data, an USB2.0 Lighting cable is required. On my iPad, an USB-C cable works for both charging and data.