Logitech’s Rechargeable Speaker S715i is a slim, black-plastic-and-metal speaker dock for iPhone and iPod that combines portability, a built-in rechargeable battery, and impressive audio quality.

Let’s start with the portability. The S715i measures 15.5 inches wide, 2 inches deep, and 5.3 inches tall, weighs just 3.5 pounds, and ships with a thin carrying bag. When you’re ready to rock, you flip out the kickstand, which, when closed, doubles as a cover for the system’s dock cradle. With the exception of the 3rd-generation iPod, the S715i works with any iPhone or iPod, and the trayless dock cradle doesn’t need any sort of insert or adapter.

On-board controls are limited: Power, Volume Up, and Volume Down. For other actions, you’ll need to use the tiny, black, infrared remote control, which offers the same buttons as well as Play/Pause, Previous, Next, Shuffle, and Repeat. I like the tactile feel of the remote, but during my testing I was a bit worried about losing it. Given its small size—less than 3 inches long, and barely 1.5 inches wide—I wish the S715i included a spot to stow the controller. (To Logitech’s credit, the included carrying bag features a pocket for the remote.)

On the back of the S715i sit just two connections, covered by a rubber tab. The first is for the included AC adapter, and the second is a 1/8-inch (3.5mm) stereo line-in jack for connecting another audio source.

When the S715i is plugged in, it charges both its own battery and your iPhone or iPod. Logitech says that after fully charging the S715i (which can take up to ten hours), you can expect to get about eight hours of battery life. This matched my testing.

Despite its small size, the S715i sports eight separate drivers: a pair of 3-inch neodymium drivers, a pair of half-inch neodymium tweeters, and four 2-inch passive radiators. (Two of those four passive radiators are rear-facing and serve as woofers.) The result? Shockingly powerful sound given the S715i’s size.

Unlike some smaller speaker systems, the S715i actually has good low-end performance. You won’t get much true low bass—it’s just not possible with 3-inch drivers—but there’s a surprising amount of “kick.” In fact, the bass this unit can put out—particularly when running from the AC adapter—is astonishingly good. And the S715i’s standout audio performance isn’t limited to the low end. I found its midrange and treble clarity to be very good, as well. (On battery power, the maximum volume and bass output decrease noticeably; even then, though, the S715i impresses.)

The biggest complaint I have about the S715i is more of an annoyance: its single status light. The light pulses whenever the device is charging, but at a lower brightness when powered off than when powered on. I had a tough time determining which level of brightness I was seeing, so I was never certain whether the speaker was on or off until I pressed the Play button.

Macworld’s buying advice

The Rechargeable Speaker S715i is an impressive portable speaker system with audio that's great both for the unit’s size and for its $150 price tag. While the audio softens a bit when running from the battery, I’m quite pleased with how good the system sounds overall.