Apple surprised us Tuesday by simply putting its latest iPhone accessory on sale. The $99 MagSafe Battery Pack isn’t the first power cell we’ve seen that uses Apple’s new magnetic system to connect with the iPhone 12 family (Anker offers a 5,000mAh pack with slower 5W charging for $45.99), but it is the first one from Apple and can charge at up to 15W while it’s plugged in.

MacRumors and 9to5Mac point out a support document that helps answer a few questions we immediately had about the device, including confirmation that this will unlock the iPhone 12’s “secret” reverse charging feature. While iFixit didn’t spot any additional hardware to add wireless charging, FCC filings revealed the company’s plan to let you charge accessories while the iPhone 12 is plugged in and charging, complete with diagrams that now look very familiar.

As Apple’s support page explains:

Charge your MagSafe Battery Pack and your iPhone

If both your iPhone and MagSafe Battery Pack need to be charged, you can charge them at the same time. Attach your MagSafe Battery Pack to your iPhone and then plug the MagSafe Battery Pack into a power adapter. Using a 20W or higher power adapter, the MagSafe Battery Pack can charge your iPhone with up to 15W of charging power.

You can also charge both if you attach your MagSafe Battery Pack to your iPhone, then plug your iPhone into a power source. You might want to charge this way if you need to connect your iPhone to another device while charging, like if you’re using wired CarPlay or transferring photos to a Mac.

If you charge your iPhone and MagSafe Battery Pack at the same time, your iPhone might charge to 80% or higher before your MagSafe Battery Pack begins charging.

Notably, reverse charging only works (so far) with this accessory, after an upcoming software update and only while the iPhone 12 is plugged in. Google’s Pixel 5 can operate as a Qi pad while plugged in, and Samsung devices have been charging anything you slap against them for a couple of years, but now Apple users can enjoy a similar feature. Will this newfound ability also charge your AirPods, Apple Watch, or anything else in the future? Apple isn’t saying (yet).

Also, in case you missed it, one image of the battery pack revealed its capacity specs: 1460mAh, 7.62V, 11.13Wh. We’ll need to do some testing to figure out exactly how much charging it can add in real life, but it’s worth remembering that in this case, watt-hours of charging is the more important figure to focus on, as seen with Apple’s old non-magnetic battery cases.