Your mobile phone is lying to you, according to Daniel Rutter at Dan's Data on Tuesday. Mobile phone battery indicators are designed to hedge towards the full side to keep the user making calls -- and spending money.

After investigating the issues behind the mobile phone's signal strength bars, Mr. Rutter turned his attention to the battery indicator.

"Battery meters are even more fun...

"It's possible to monitor the charge in a battery - any kind of battery - with considerable accuracy. There's a certain amount of guessing involved, because the 'fullness' of different battery chemistries doesn't necessarily map well to terminal voltage even if the battery's powering an unchanging load. But modern 'smart' batteries with little chips on them that keep track of how long they've been lasting lately really do work pretty well."

With that technical knowledge, mobile phone makers, given a choice, would like the user to think that there's just a little more charge than there really is. There's ample motivation for this:

"Reason one: A battery that stays (apparently) full for a long time makes a phone look good. Even if it doesn't actually deserve to.

"Reason two: When your phone still (apparently) has lots of charge left, you're more likely to use it. People who think their phone's going flat will make fewer, and shorter, calls. And that makes phone companies sad."

No one, to this reporter's knowledge, has done extensive testing on the iPhone battery to test this hypothesis. Perhaps it's because Apple has elected to simply show vague graphical indicators of the iPhone battery charge instead of a numerical percentage available on the MacBooks.

"This is a particular problem in the U.S. market, where most mobile phones are not just usually locked to one provider, but also customised for that provider, with specific firmware that can very easily include a battery meter that has an even larger Lie Factor than usual, "Mr. Rutter concluded.