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Some brands of laptop have less than half the battery life promised by their manufacturers, a study by consumer group Which? has found.

Only Apple's Macbook Pro lived up to its 10-hour battery life claim in the tests, which included watching films and using the net via wi-fi.

Models by Dell, Acer, Lenovo and HP came in with around half the advertised battery life.

Manufacturers tend to test in "optimum conditions", one analyst told the ´óÏó´«Ã½.

"Battery life metrics on consumer electronics devices such as laptops are typically measured in optimum conditions, which maximise performance," said Ben Wood from CCS Insight.

"There are lots of variables when it comes to real world use such as how bright the screen is and what applications you are using, which can have a major impact on battery performance."

Dell also told Which? it was difficult to define average laptop use.

"Every individual uses their PC differently," it said.

"It's similar to how different people driving the same car will get different mileage depending on how they drive."

by seven different manufacturers.

It found that:

Repair firm Geek Squad said it often serviced laptops suffering low battery life within one to two years of purchase.

"We find there is a direct correlation between the amount of software running on the machine at any given time and the life a user should expect from it," the firm said.

It recommends lowering screen brightness, turning off features such as bluetooth and wi-fi when not in use, and making use of power-saving software, which is installed in many Windows and Mac-based devices, to maximise battery life.