If it ain't broke... make it slightly better.

At least, that's what OnePlus is saying with the OnePlus 3T -- a phone that comes just five months after the company launched its OnePlus 3 flagship in June.

The OnePlus 3 was our favorite mid-price phone until this 3T came along. I have no idea why the company is in such a rush to replace its already excellent phone so soon after its launch, but there you have it. And here you have a phone that's the new standout in its category. Oh and don't worry -- the 3 is far from obsolete.

Compared to the 3, the 3T has a darker grey color and a new 128GB storage option (there's also a special-edition black version too). It's got a faster processor, a bigger battery and a better front-facing camera. It's also a smidge more expensive at $439 or £399 for the 64GB variant and $479 or £439 for the 128GB model. (OnePlus isn't available in Australia, but that converts to about AU$580 and AU$632.)

For OnePlus 3 owners, don't panic. You're only missing out on a couple hours of extra battery life and better selfies. Plus, all the 3T's new software goodies will soon roll out to 3 owners too. Read on for more details about how the 3T is different (including our spec and price comparison chart at the end), and check out our full OnePlus 3 review for an even deeper dive.

The OnePlus 3T's darker shade of grey See full gallery

Still as fast, and now lasts longer

The earlier OnePlus 3 was fast -- it outpaced the Samsung Galaxy S7, LG G5 and HTC 10 in diagnostic benchmark testing scores. This time around, the 3T beats the 3 in the same benchmarks and is just as fast as the Google Pixel and LeEco LePro 3 -- two newer phones that have the same Snapdragon 821 processor as the 3T.

When it comes to real-world use, the camera opens and snaps a shot in seconds. You'll scroll through a webpage and navigate the phone without lag. The keyboard is as quick and responsive as you'd expect. If you plan to download a lot of apps and fill up storage with photos and video, you may want to get the 128GB version to give yourself some breathing room. A nearly full 64GB phone could slow down operations later on.

OnePlus gave the 3T a bigger battery than the 3: 3,400mAh instead of 3,000mAh. As expected, it lasts longer. In our lab tests for continuous video playback on Airplane mode, the 3T lasted an average of 16 hours and 56 -- a notable 2.5 hours longer than the 3.

The battery still uses OnePlus' proprietary Dash Charging technology, which charges the battery quickly without overheating. In 30 minutes, the phone charged up to 57 percent, and after an hour, reserves were at 93 percent. A full charge took about 1 hour and 35 minutes. This is about 20 minutes longer than the 3, but that makes sense given the increase in size.