Nokia admits some problems with N73 lithium batteries that they may swell up. You could check this Nokia web site to see if you’re affected.
Nokia coughs to ballooning batteries
Nokia has admitted that some customers are seeing BP-6M batteries, as used in the N73 handset, ballooning to several times their original size, and in some cases to such an extent that the phone case won’t close.
El Reg first heard about the problem from a reader just after Christmas, and Nokia has been investigating since. Today the company assures us that the issue is nothing to be concerned about, and customers who find their batteries bulging should nip down to their nearest service centre for a free replacement.
Nokia isn’t saying how common the problem is, only that it affects a “limited number of batteries” and that the swelling presents “no risk to health of safety” – assuming of course that your health and safely doesn’t depend on having a working telephone before you have a chance to switch batteries. (Source: The Register)
Batteries swells are hardly unheard of. Affected batteries can be exchanged.