A study by consumer group Which? has found that some brands of laptop are claiming their batteries last twice as long as they do in reality.
Only one laptop, Apple’s Macbook Pro, achieved the claimed battery life in the Which? tests, which included watching films and surfing the internet.
Models by Dell, Acer, Lenovo and HP came in with around half the advertised battery life.
One analyst told the BBC that this was because laptop manufacturers tended to test in “optimal conditions”.
“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.”
The Which? tests found that:
The Acer E15 lasted two hours, 56 minutes (claim: six hours)
Apple’s MacBook Pro 13 lasted 12 hours (claim: 10 hours)
Dell’s Inspiron 15 5,000 lasted three hours, 58 minutes (claim: seven hours)
HP’s Pavilion 14-al115na lasted four hours, 25 minutes (claim: nine hours)
Lenovo’s Yoga 510 lasted two hours, seven minutes (claim: five hours)
Repair firm Geek Squad said it often had to service laptops for poor battery life within a year or so of the original 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.