LAS VEGAS—Do you forget to charge your phone? The latest new device from low-cost unlocked smartphone maker Blu, the Studio Energy, might be for you. I took a look at it and its super-slim cousin, the Vivo Air, here at CES.

Blu makes cheap phones with a twist. They could be really bright colors. They could be Windows Phones. Or, as is the case with the Studio Energy, they could pack a ridiculous 5200mAh battery that's double the capacity of the batteries in most other 5-inch phones, allowing for four days of standard usage and 45 days of standby time. The battery's so big that you can use it to "reverse charge" your other devices off the phone.

For a phone with such a monster battery, it's surprisingly slim and portable. If you hadn't told me the Energy had the big battery in it, I would never have guessed; it's still only 10mm thick.

Beyond the big battery, Blu keeps things relatively simple to maintain a $179 unlocked price point. The Studio Energy runs Android 4.4 for now; it'll get an upgrade to Lollipop soon. It's a pretty stock version of Android, although Blu added a system-cleaning app and a few widgets.

It's using a 1.3GHz Mediatek quad-core processor, and it runs on the AT&T and T-Mobile 3G networks. (It's better for AT&T than T-Mobile, though – it only has HSPA+ 21 rather than 42, and it lacks the 1700 band.) Being a 3G phone rather than an LTE device, while slowing Internet speeds, may also help extend the Studio Energy's battery life.

The screen is a pretty average 720p IPS LCD, and the phone has 8-megapixel and 2-megapixel cameras, plus a MicroSD memory card slot and two SIM card slots.

I spent a little time with the phone, and other than the battery and the price, it's not that memorable. But the battery and the price are so memorable! It's okay to do a few things well, as long as you do other things adequately.

The Studio Energy will go on sale in late January unlocked on Amazon.com