Smartphone battery life has come a long way in recent years, and nowhere is that more true than in Asus' ROG Phone series. This series of gaming smartphones always seems to be at the top of our best smartphone battery life list, and despite breakthroughs like the iPhone 16 Pro Max, no one seems to be able to keep up.

But now that the Asus ROG Phone 9 Pro has arrived, the question is whether the Asus ROG Phone 8 Pro will impress the same way that the Asus ROG Phone 8 Pro impressed us in our custom battery life test last year, when it recorded about 19 hours. The short answer is yes.

In our battery life test, we continuously reload a web page with the screen brightness set to 150 nits over a 4G cellular connection. This process continues until the phone's battery runs out, earning a spot on our list of best cell phone battery life, meaning that we are in the top 15 for the longest results recorded in the test.

Currently, a phone must last about 14 hours to have a chance of making the list. And happily, the Asus ROG Phone 9 Pro met this goal with plenty of time to spare, lasting 20 hours and 34 minutes before the battery ran out.

This is an incredibly impressive battery life, more than 100 minutes ahead of the previous No. 1 Asus ROG Phone 8 Pro. However, this is with the screen set to automatic refresh rate, and if the ROG Phone 9 Pro were constantly locked to a maximum refresh rate of 185 Hz, it would not achieve such great results. Still, no matter what other phone companies do with their batteries, Asus always seems to be one step ahead.

The ROG Phone 9 Pro doesn't just beat out its predecessor. It also knocked some of 2024's biggest and best smartphones further down the best battery life list. That includes the iPhone 16 Pro Max, which clocked in at 17 hours and 17 minutes and did so well in the battery test that we had to redo the test multiple times to make sure it wasn't just a fluke.

The result of 20 hours and 34 minutes beats the OnePlus 12 and Samsung Galaxy S24 Ultra's 17 hours and 5 minutes and 16 hours and 45 minutes. the ROG Phone 9 Pro even beat the OnePlus 12R. the OnePlus 12R has a much larger battery than the other three models. The OnePlus 12R has a much larger 5,500 mAh battery, comparable to the Asus ROG Phone 8 Pro. However, its 18 hours and 8 minutes of battery life is not as long as the new No. 1 model.

Battery performance like this doesn't come out of nowhere; the Asus ROG Phone 9 Pro has a huge battery rated at 5,800 mAh, which we expect to last longer. This battery is 300 mAh larger than last year's model.

It should also be noted that the ROG Phone 9 Pro is one of the first phones to run on the new Snapdragon 8 Elite chipset, manufactured in a 3nm process. This process means smaller chips, allowing for better chip performance while reducing energy consumption, a key factor in extending battery life.

In the unlikely event that the ROG Phone 9 Pro unexpectedly runs out of battery power, it can rely on an impressive 65W wired charging speed. According to our tests, it restored 37% of battery life in just 15 minutes and 74% after 30 minutes. Wireless charging, however, is not as impressive, and the 15W wireless charging speed seems to take a long time to make a dent in such a large battery.

It will be interesting to see how competitive products fare in the coming months against the Asus ROG Phone 9 Pro's impressive battery life. Especially if it is powered by the Snapdragon 8 Elite. But for now, if you're looking for the best battery life, you might want to check out Asus' offerings.