Qi vs. PMA
There are two major standards for wireless charging: PMA (Power Matters Alliance) and Qi (pronounced “chee”). If you see a charger that only supports PMA, keep moving. The new iPhones only support Qi.
Fortunately, Qi is by far the most common standard for consumers, so you shouldn’t have much trouble finding a compatible charger. What’s more, every Qi compatible charger should work just fine with every iPhone from the iPhone 8 onward, even if it doesn’t specifically list support for them on its packaging or marketing materials.
5W vs. 7.5W performance
The new iPhones shipped with initial wireless charging limited to just 5 watts. That’s pretty slow, but then again, the in-box power adapter is also only 5 watts. So wireless charging really isn’t any slower than the (admittedly pitiful) power adapter that comes in the box.
The iOS 11.2 update increased the maximum wireless charging speed to 7.5 watts. That’s 50 percent faster, but charging speeds vary, and they slow down a lot as the battery gets full. Still, if you want the best performance in a wireless charger, look for one that can support 7.5 watts or more. Some pads support faster charging speeds only on some Android phones, but are limited to 5 watts on iPhones.
For pads that don’t come with fast-charging adapters, you’ll want to look at the store pages to see what is required to enable higher-speed charging. Some enable faster charging only when using an adapter with Qualcomm’s Quick Charge technology, some work with any high-wattage USB power adapter (like the iPad adapter Apple sells). See what is required before buying a new adapter.
Flat or standing?
You’ll see two types of wireless chargers on the market: flat pads, and angled stands. A flat pad is simple and easy, but you might want to consider a stand. With a stand it’s a lot easier to use your phone while it’s charging up.
And with iPhones that have Face ID, a standing charger makes it easy to unlock your phone without picking it up.
Portrait and landscape orientation
If you get a stand instead of a flat charger, you’d be wise to make sure it’s made to work with your phone in both landscape and portrait orientation.
Most of the time, you’ll plop down your phone standing upright. And Face ID on iPhones will only work when the phone is upright, too.
But a charger that works well with your phone in landscape mode makes it easy to play certain games, and of course watch videos, without taking your phone away from those precious free electrons.
If you keep a case on your phone, you shouldn’t worry too much about whether it will work with a wireless charging pad or stand. The vast majority of cases will work just fine.
There are three types of cases that can pose problems, however:
The first is a case with a metal back (or a battery case). That battery case may seem attractive with its extra 5,200 mAh of extra juice, but it won’t work with wireless chargers.
The second is a wallet case. A particularly thin one might actually work, but electromagnetic induction and credit card magnetic stripes just don’t mix. If you don’t want to screw up your cards, don’t put them between your phone and a wireless charger.
The third is especially thick cases. Most chargers will work fine with any case up to about 3mm thick, and some can go through a 5mm case with ease. But maybe you’re a demolition derby racer and also work construction plus you’re a rodeo clown on the weekends. Maybe you have an extra-rugged case. If so, it’s probably too thick to get a wireless charge going, even if it doesn’t have a metal back (as many extra-rugged cases do).
I have written professionally about technology for my entire adult professional life - over 20 years. I like to figure out how complicated technology works and explain it in a way anyone can understand.