For those of us who follow iPod accessories, it's difficult to believe that it's been nearly four years since Bose's original SoundDock was released, making it one of first "desktop" speaker systems for the iPod. Perhaps just as surprising is that while most of the other big vendors of iPod gear have revised their speaker lines several times over that period, Bose has continued selling essentially the same SoundDock, at the same £199 price, that it released back in 2004.

So when Bose announced a new version of the SoundDock, I expected it to be a replacement for the original. Instead, Bose added a second product to the SoundDock line: the £299 SoundDock Portable. True to its name, the SoundDock Portable is in many ways simply a portable version of the original SoundDock; however, it does offer a few unique features.

Available in either black or white with a silver front grill, the SoundDock Portable is just slightly smaller than original at 17.1cm high by 30.6cm wide by 15.4cm deep when closed for travel; it weighs a hefty - for a portable system – 2.37kg. The Portable retains the full-frontal-grill design of the standard SoundDock, but includes several aesthetic and functional changes.

For starters, the Portable's dock cradle, which adopts Apple's Universal design, rotates into the body of the SoundDock for travel. Unfortunately, unlike most iPod speaker systems using a Universal dock, Bose doesn't include dock adapters for older iPods. (With the proper adaptor - available from Apple if your iPod didn't include one - the SoundDock Portable works with all dockable iPods back to the original iPod mini. The iPhone is also compatible, although you may experience audible interference if you don't put the iPhone in Airplane Mode.)

The Portable also includes touch-sensitive Volume Up and Volume Down buttons, located on the right-hand side of the system. Separating these buttons from the dock cradle, where they were located on the original SoundDock, is useful thanks to another new feature: an auxiliary-input jack, located on the back of the unit, that lets you connect another audio device. You can listen to an external audio source even if the Portable' dock cradle is collapsed inside the unit; in fact, to listen to a source connected to the auxiliary input, you need to first remove your iPod or iPhone from the cradle. Also on the back of the system is a bass port that doubles as a handle - a nice touch that makes it easier to carry the system.

But the biggest new feature is the Portable's rechargeable, lithium-ion battery, which lets you take the system to locations not blessed with electrical outlets. Bose claims the battery provides three hours of playback at full volume - an interesting approach to rating, given that most vendors provide battery-life figures based on "typical listening volume" (a euphemism that generally means "not too loud").

To Bose's credit, when listening to an audio system outside, you need to crank the volume considerably higher than you do inside to get a comparable listening level, so the company's worst-case-scenario estimate errs on the conservative side. But I never needed to turn the volume full-blast when outside, which means I saw much longer playback times in my testing. If you'll be listing at relatively modest levels, you can expect well over 10 hours of playback.

Interestingly - and unlike most portable iPod speaker systems - the SoundDock Portable charges your iPod or iPhone even when the system is running off battery power; most speaker systems charge your iPod or iPhone only when the system is connected to AC power. The battery is also easily replaceable; you need only a small coin to unlock the battery and swap it with a fresh one. Bose sells replacement batteries for £69.

A small light, located behind the metal grill just above the Portable's iPod dock, indicates various statuses - powered on, charging, low battery, and more - depending on the light's colour and whether it's solid or blinking. This indicator is useful, but I found it difficult to remember what the various colours and states meant.