Most of us plug our phones in to charge them. But there is also wireless charging available in some devices, which uses a charging station to transfer energy to the receiving device via electromagnetic induction.
So what is reverse wireless charging? The ability to turn the tables; for a wireless charging-capable phone to act as the charging station and be used to charge another wireless device. Be that another phone, or wireless headphones like the Beoplay E8 MkII.
However, it's a feature in its infancy, first offered by Huawei in the Mate 20 Pro, then by Samsung with the S10 series launch, with other flagships expected to follow in the future.
How fast is reverse wireless charging?
First thing's first, reverse wireless charging isn't quick. This is a low-power solution that's for emergency top-ups really - like when your friend has forgotten a cable and is down into 'danger 5 per cent' territory. Or for getting some extra juice into those wireless charging headphones (we expect more of these to arrive in the future).
Quick charge technology - i.e. when using a cable - has been progressing over the years. At best there's Oppo's Super VOOC, which can manage 10V/5A (50W). It'll charge a 3000mAh battery in about 30 minutes.
Qi wireless charging isn't as quick, with 20W possible - although most charges at 10/7.5/5W, thus slower. Typically that'll mean around 120 minutes to charge a 3000mAh battery.
Reverse wireless charging doesn't have a set standard and neither Huawei or Samsung has released the specification. Needless to say, however, it's slower still. Plus the source device will have a limit on how much energy it can output from its battery before that depletes.
Which phones offer reverse wireless charging?
Huawei Mate 20 Pro
This phone debuted reverse wireless charging. Huawei's Mate 20 Pro can charge any other Qi wireless device, irrelevant of brand, when the feature is set active and the two devices are paired back-to-back.
Huawei P30 Pro
The next step in Huawei's evolution, the P30 Pro is similar to its Mate cousin, albeit with a quad camera setup that's gunning to be the best in the business. It's only just been announced, however, so isn't available to buy just yet - but it's coming very soon.
Samsung Galaxy S10 / S10+ / S10e
Not content with just one phone to offer reverse wireless charging, Samsung has gone with all three models in its S10 range. There will also be the S10 5G in mid 2019. The real take-away here, however, is that the Galaxy Buds will offer wireless charging, so it'll be possible to recharge your headphones directly from the phone, without wires, should they run too low.
Which phones can be charged by reverse wireless charging?
If you don't own a Huawei Mate 20 Pro or Galaxy S10 model - and the Huawei P30 Pro doesn't take your fancy - then you currently can't charge other devices using reverse wireless charging. If a friend or colleague does own one of these phone, however, then there's no limit on what can be reverse charged - so long as it's Qi wireless charging compatible.
That includes (among others not listed here) the Apple iPhone 8, 8 Plus, X, XR, XS, XS Max; Samsung Galaxy Note 9, S9, S9+, Note 8, S8, S8+; Google Pixel 3, 3 XL; Huawei Mate 20, Mate 20 Pro; Xiaomi Mi Mix 3; Sony Xperia XZ3, XZ2; LG G7 ThinQ, V30; and Nokia 8 Sirocco.