If you find the 12.9-inch iPad Pro’s lengthy charge times to be a real pain, then you need Apple’s new USB-C to Lightning Cable and 29W power adapter. According to in-depth tests, the new USB brick can charge your supersized slate more than twice as fast as the default adapter.

At $49, Apple’s 29W USB-C power adapter isn’t exactly cheap — and you’ll need an additional $25 to purchase the new USB-C to Lightning cable that’s required to charge iPad Pro. But if you often need to top up your iPad Pro quickly, it’s really the only fast-charging solution.

And it works! Tests carried out by Federico Viticci over at MacStories show that charging the 12.9-inch iPad Pro with the 29W power adapter is significantly faster that using the default 12W adapter. Whether the device is idle or in use, the difference is huge.

Viticci used a custom app developed by Instapaper creator Marco Arment — which isn’t available in the App Store — to measure charging times in 10-minute intervals from 0 percent to 80 percent. Why 80 percent?

Because between 0 percent and 80 percent, Apple’s devices charge faster than they do between 80 percent and 100 percent. For that last 20 percent, charging slows to what Apple calls “trickle charge,” which helps extend the lifespan of your device’s lithium-ion battery.

The chart below shows Viticci’s measurements during different tasks. For example, while the iPad Pro took 213 minutes to charge to 80 percent with the 12W cable and the display turned off, it only took 93 minutes with the 29W adapter under the same conditions.

The different is even greater when the iPad Pro is in use. While sat at the home screen with brightness at 100 percent, the device charged to 80 percent in just 107 minutes with the 29W adapter, but it took a whopping 732 minutes to reach 80 percent with the 12W adapter.

Viticci also found that while playing the graphically-intensive game Oceanhorn at full brightness, the 29W adapter charged the iPad Pro by 5 percent in ten minutes. In comparison, the 12W adapter charged it by just 1.2 percent.

Another interesting difference is that while Night Shift mode slows charging with the 12W adapter, it has no affect when using the 29W adapter.

“The 29W adapter is remarkably consistent in battery gains in a variety of conditions and it dramatically reduces the amount of time required to charge the iPad Pro,” Viticci concludes. “The 12W power adapter essentially brings glorified iPhone charging to the iPad Pro – a subpar experience that, at this point, is barely acceptable.”

Viticci argues that Apple should bundle the 29W adapter with iPad Pro instead of the 12W adapter. Unfortunately, that’s not going to happen any time soon, so you’ll have to buy the adapter and USB-C to Lightning cable separately.

It’s worth remembering, however, that this 29W adapter is exactly the same one you get with the 12-inch MacBook. If you already have one of those, then, you only need to buy the USB-C to Lightning cable to get fast-charging for your iPad Pro.

It should also be noted that the 29W adapter can only be used with the 12.9-inch iPad Pro — not the new 9.7-inch model.