For almost two years, I've been singing the praises of the UE Boom to anyone who asked. The cylindrical speaker is one of the absolute best-sounding, best-designed portable Bluetooth soundsystems, a product category unfortunately overpopulated by awful, bromidic barf machines.

Funny thing is, the UE Boom is a me-too product. It came along well after the Jawbone Jambox, the diminutive Bluetooth speaker responsible for setting fire to the category and generating a giant, candy-colored wave of mobile boombox hysteria. But I've always preferred the UE Boom over the Jambox, or other competing speakers like the Bose Soundlink Mini. The UE Boom doesn't just sound better, it's got a smarter design. The cylindrical shape throws sound in a wider arc than the forward-facing drivers found in the brick-shaped enclosures. And, the UE Boom's tiny circular footprint keeps the speaker from "walking" around on your countertop as it vibrates—an inconvenience of Jawbone's speaker that becomes a fatal flaw if you place it too close to your bathtub or kitchen sink.

But the Jambox has a big brother to bail it out of schoolyard battles: the Big Jambox, basically a super-sized version of the original Jambox. It sounds awesome, has much better battery life, and is massive enough to stay put when you pump up the volume. It's Jawbone's winner.

So in response, Ultimate Ears has done exactly what everyone expected it to do: release a bigger UE Boom. That's all the UE Megaboom is: a much bigger, much louder, and much better-sounding UE Boom. It's also my new favorite Bluetooth portable.

The original UE Boom is about the size of a tallboy can of beer. The UE Megaboom is the same shape, but scaled up from 7 inches tall and 2.5 inches wide to 8.5 inches tall and 3.25 inches wide. It weighs just under two pounds, and it's satisfyingly beefy. Also, one very welcome upgrade is that the Megaboom is fully IPX7 certified. That means it's entirely waterproof—rubber doors on the bottom seal the USB charge port and the 3.5mm input jack—and able to sustain a tumble into the tub or jacuzzi. It also makes it the preferred companion in a sweat lodge, on a beach trip, or in a hot yoga class. Also on the bottom is the same folding D-hook that you can use to hang it from the roof of your tent. Unscrewing that D-hook exposes a threaded post mount that fits a tripod or a gooseneck.

The UE Megaboom costs $300. Liana Bandziulis

A full charge on the battery earns you a claimed 20 hours of use. Oddly, in my testing, I got closer to 25 hours of continuous play out of a full charge. Actually, when I first received my review unit, I fired it up without charging it. Once paired to my phone, the Megaboom's tiny battery indicator in my iOS status bar registered less than half full. I figured I'd get three or four hours out of the current charge. I got almost ten. I brought it on a week-long road trip, charging it to full before leaving. I didn't even need the charger. I could have left it at home.

People can quibble forever about the audio quality you get out of these Bluetooth speakers, and whether any of them are any good. But I can tell you I exited a month of testing the Megaboom with zero complaints. I listened to an auditory salmagundi—modern rock, jazz, acoustic guitar, John Zorn, Aphex, classic Nashville, the first five Black Sabbath albums, the last two episodes of Serial—and everything sounded just great. Keep in mind I've been testing these things since before the Jambox came out, and I've heard some truly terrible-sounding Bluetooth speaker boxes. This one excels.

If you want to futz with the sound, UE makes a bespoke app (iOS and Android) with a standard EQ. It also adds an alarm feature and the ability to remotely power up the speaker just using your phone—I liked that I could turn it on from across the room without getting out of bed. There's also the "Double Up" feature, which lets you join a pair of Booms or Megabooms, running them either as two synced stereo speakers, or as a true stereo pair with one playing the left channel and the other playing the right.

All this for $300, the same price as the Big Jambox. But I think the UE Megaboom is the better buy. It has a smart waterproof design, a small footprint, excellent battery life, and it tosses clear, lively sound in a nice wide arc. It's the best battery-powered speaker for almost any mobile application, inside or outside the home.