Apple has declared war on its portable audio rivals by cranking up the iPod's battery life – but it's actually underestimating the real figure. What's the deal with that?

Time was when you knew where you were with battery claims. You just took whatever the maker of your MP3 player said with a pinch of salt. They weren't lying, mind you – no doubt you could achieve a similar figure if you turned the volume right down and switched off all the extraneous features and didn't power on the screen at any point and tried the experiment 16 times and used the best result. And ran the test on an old Indian burial ground (possibly).

Anyway, we noticed things had changed when we reviewed the SanDisk Sansa e260 a couple of issues back. The battery was supposed to last for up to 20 hours, but it just kept on going, approaching the 22-hour mark. Then the next month the Creative Zen V blew our minds by managing 17 hours after the maker claimed only 15. Whatever next?

A few weeks ago Apple squeezed out its redesigned iPod nano (reviewed in December's PC Advisor, available from 19 October, plug fans!) and made a bold declaration: its battery life was a monstrous 24 hours. The first-gen nano could manage only about 13, so we were sceptical. But our tests ranged from 26 to a colossal 29 hours, putting the nano right up there with the Samsung YP-Z5, the record holder in this department. Exciting stuff.

So why are the audio manufacturers becoming so coy about this crucial aspect of their products? We have a paranoid conspiracy theory you may find interesting.

Companies undersell battery life because they know that after all those years of gentle exaggeration, most customers check a magazine or an esteemed website such as this one to find out the real figure. So the makers manage to look honest – even modest – without missing out on the PR of having the best battery around.

The best thing about the tactic, of course, is that the maker of the audio player can't legally be held to the results of journalists' tests – so if the battery starts to degrade after a year or so, the warranty won't kick in until it drops below the claimed value, not the real-world one. Clever, isn't it? It's like getting other people to do your boasting for you.