Apple has admitted that some batteries in its Macbook and Macbook Pro line of laptops have 'performance issues' and has issued a software update to fix the problem.

Among the symptoms of batteries that are affected are swelling, the battery not being recognised or not charging, and a shorter than expected battery life.

The company said that the problem, which could affect any laptop or batteries bought between February 2006 and April 2007, 'is not a safety risk' and has offered to replace any defective batteries. In the meantime, users could continue to use their current battery, Apple said.

Reports of swollen batteries have circulated since the Macbook range was introduced early last year and 'visibly deformed' battery packs were among the problems the update was designed to address, the company said.

If symptoms persist after the update, which can be downloaded here, users should contact their local store to arrange for replacement battery free of charge, Apple said.

Despite the problems, Macbook remains a successful range for Apple. The company recently reported that sales of its portable computers rose from 498,000 to 891,000 over the 12 months to March 31, helping boost quarterly profits to $770 million (£386 million).

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