Why's my cell phone melting?

Cell phone maker Nokia warned Friday that a growing number of its handsets are being damaged by badly made or counterfeit batteries from other companies.

The number of phones destroyed by so-called third-party batteries, sold by street vendors or on the Web, have risen enough since December to prompt a warning from Nokia, said company spokesman Keith Nowak.

The batteries usually don't have circuitry to shut down the power source once it begins overheating, Nowak said. Enough heat can be generated to melt a phone's plastic casing and the circuits inside, he said.

"People really shouldn't use anything but a Nokia-made battery inside any of our phones," he said. "If a third-party battery is made improperly and destroys a phones, it's not going to be covered under warranty."

Nokia handset owners in Asia, Africa and Europe have reported problems, Nowak said. There have not been any problems in the United States, he added.

The handset maker did not name specific battery makers to watch out for.

Nokia appears to be acting out of genuine concern, rather than using the warning as a scare tactic to keep customers from buying phone accessories made by other companies, said Joel Tax, an analyst with research firm Santa Clara Consulting Group.

"Selling accessories (like batteries or chargers) has not been a big deal for Nokia, so we might be looking at something pretty bona fide on their part," he said.

Cell phone manufacturer Motorola is unaware of any increase in its phones being destroyed by third-party batteries, said Alan Buddendeck, a company spokesman. But the problem remains a persistent one, he said.

"It's fair to say that it happens with sufficient frequency," he said.