Nokia is offering to replace up to 46 million batteries for their mobile phones due to reports of overheating while charging.
From the WEB site
“This is a product advisory for the Nokia-branded BL-5C battery manufactured by Matsushita Battery Industrial Co. Ltd. of Japan between December 2005 and November 2006. This product advisory does not apply to any other Nokia battery.”
There have apparently been very few cases of reported problems however more info and a product guide can be found here