Amazon has bumped the battery life and added native PDF support for its 6-inch Kindle ebook reader on Tuesday via a firmware update following a 6 month firmware improvement and testing program.

The news means that the Kindle now has battery life of up to 7 days with wireless turned on, compared to 4 days. According to the company, battery life with wireless turned off can be up to 2 weeks.

Amazon has also announced that the 6-inch Kindle now has a built-in native PDF reader that enables Kindle customers to read their own documents, something other ebook readers have been able to do from the start.

To read their personal or professional documents, Kindle customers will have to email PDFs to their Kindle email address or move them over using a USB connection.

Customers that prefer to have their PDF documents converted to the Kindle format simply type "Convert" in the subject of the e-mail when sending documents to their “@kindle.com” address.

The firmware update, which will come as standard to all new Kindles will be sent out automatically via Whispernet wireless to models already in use.

However not all will get the Native PDF support, says Amazon.

"It will also be available for some earlier versions of Kindle via an automatic Whispernet wireless firmware update", the company said in a statement.