I think I may have some words to eat. Unlike some notebook users, I actually use mine on the move. It's not a desktop PC with a built-in UPS, it's genuinely mobile. And it has to have a battery that works.

When IBM read my comments about nine months ago expressing some scepticism about the future of the Centrino and its abilities to double battery life, I was keen to expose them and their absurd claims.

They said: "Would you like to test the ThinkPad X31?" I said: "Yes!" and started sharpening my teeth and claws.

The law of portable PCs has been known for ages. You get about two hours of battery life, and then it shuts down.

When I'm out and about, I use a Wi-Fi card connected to the nearest hotspot, or plugged into GPRS data. I have IRC and instant messaging programs running, with people constantly popping up asking questions or providing answers.

I run my own website and it involves frequent access to the site, FTP uploads and a Python script which chews up CPU cycles and disk access. On top of that, there's text editing, note taking, photo processing ... my machine has to WORK.

My own machine is a ThinkPad X22. It's nice, but its standard battery is lucky to last two hours. The X31 looks and feels very like the X22, but costs nearly a thousand quid more.

It has virtually the same hardware, plus a couple of extras like FireWire and a parallel port. But you do get a Pentium-M processor and the rest of the Centrino package. And the promise of Centrino was that it would extend battery life.

I've heard this all before, frankly. When the first Centrino leaks emerged a year or so ago, Intel played down the amount of difference it would make.

Intel correctly pointed out that the processor and chipset couldn't account for more than 30 per cent of the battery drain on a notebook with a big display and a disk.

So I warned my readers that they shouldn't get too excited about Centrino. It would reduce power consumption, yes; but not by that much.

Then IBM sent the X31, and with it the large, high-capacity battery, so I took it with me to a seminar in Barcelona.

It's a small machine with a small display - a nice, bright display, but it's not a rival to Apple's DVD cinema portable. I charged up the battery overnight and resolved to leave the power supply behind.

At 7:45 I switched it on, logged onto the wireless Lan and began work. I made verbatim notes, posted items on my Weblog, discussed the presentation with other delegates over IRC, wrote news items and posted them to my website.

I interviewed people during each and every break. At 16:30 the warning message appeared: 'You have only 10 per cent of your battery capacity remaining.'

That's the breakthrough. For me, it's the Holy Grail. IBM's marketing figures claim 11 to 13 hours battery life, which is piffle. But who cares if you can really get eight hours or more of solid work out of a portable PC?

That's a day's work. That's a transatlantic flight with urgent deadlines. All without having to find a power outlet. Okay, the battery is a lump, but the whole package is still a comfortable weight in your backpack or briefcase.

I've never, ever, written a PC review before that ended: "They're going to have to fight to get this machine back," and I'm not going to do it now.

But this is the first notebook I've handed back with a genuine regret that my current one isn't due to be replaced for another year.