Unlike the Trust power adapter, this product acts as a replacement or additional battery for a notebook computer, but in many ways it's similar.

Rather than sliding into the battery's place inside the notebook, the Universal Notebook Battery stays outside, connecting to the notebook using the power connector.

The battery sits between your computer and its power adapter (or a compatible adapter such as the Trust model), and charges up along with the computer's internal battery.

Once it's charged (a set of lights on the battery show the charge level) it can be used to power the computer, or you can detach it and store it for use when the computer's internal battery has run out.

That makes it very useful for travellers who won't be able to recharge from the mains often, but because it's external it does add a bit of bulk to the amount of kit you'll be carrying. The helpful and clear manual lists several notebooks that work, but although ours wasn't listed it still functioned fine. The plugs and sockets are coded with matching letters so you can easily tell which ones are required for your notebook.

The '50' in the product's name refers to the number of watt-hours of power it can produce, which will vary depending on the notebook, but on our test system it was able to provide enough power for an hour's work.

The Universal Notebook Battery works very well, but its price makes it a luxury unless you regularly find your computer's battery is being squeezed dry.

Vista compatible: n/a