Apple has released a software update designed to improve performance problems the company has identified that can affect some MacBooks and MacBook Pros.

Battery Update 1.2 (244K) aims to repair a number of problems, the company explains in this note on its website.

"Apple has recently discovered that some batteries used in its MacBook and MacBook Pro notebooks may have battery performance issues," the report explains.

The update is designed to improve performance, and is available through Software Update or for direct download from its support website.

The update should be run on all MacBook and MacBook Pro computers and extra batteries that were purchased between February 2006 and April 2007.

The company stressed that the batteries used pose no safety risk – you can continue to use your battery securely.

The company is also offering free battery replacement for users whose batteries exhibit any of the following problems after the update is installed. Free replacement is available "for up to two years from the date of purchase of the computer," the company said.

Replacement checks can be conducted at Apple retail stores, Apple Authorised Service Providers and can be arranged using Apple's telephone support.

Affected batteries will have one or more of the following symptoms:
– Battery is not recognized causing an “X” to appear in the battery icon in the Finder menu bar.
– Battery will not charge when computer is plugged into AC power.
– Battery exhibits low charge capacity/runtime when using a fully charged battery with a battery cycle count (as shown in System Profiler) of less than 300.
– Battery pack is visibly deformed.

MacBook or MacBook Pro batteries that don't have any of these symptoms won't need to be replaced.

Once the update has been installed, each battery inserted into your laptop will automatically be updated, but you must have the power cable connected and plugged into a working power source.