In the past, investigations have proved batteries bursting into flames have caused air disasters. So, if batteries can bring down a plane they can burn down your home.
A lot of us throw our old batteries in a drawer because we know we shouldn't throw them in the trash. But while they are waiting for recycling they're dangerous.
"All batteries have a positive and a negative terminal and if you bridge across the positive to the negative terminal you will generate a flow of electricity," Batteries Plus Bulbs shop owner Bill Perin said.
Finney: "You've actually put these two together."
"They will clip together. So it's possible that those things could be jammed together in a drawer," Perin said.
Finney: "OK, they are getting hot already."
"Yeah, so that's where the danger comes in; the heat," Perin said.
Finney: "It is like a hand warmer now."
"It is. And it will just keep getting hotter and hotter and hotter," Perin said.
San Rafael Fire Department Environmental Management Coordinator Courtney Bell says she worries about these things.
"We collected last year almost 100,000 pounds of batteries at the household hazards waste facility. Yeah, it's a lot we get a lot of batteries," Bell said.
She says batteries can combust into flames. Not often, but it happens.
"It is unusual for batteries to cause fires, but it definitely is a possibility and we want people to know that storing them properly is easy and it is easy to prevent a fire," Bell said.
So how do you protect yourself? Put the batteries back in their original packaging if it's available. If not, protect your depleted batteries using common household tape.
"Just pull off a piece of tape and you just put the tape across the top terminals and then do the same with the bottom terminals," Perin said.
San Rafael has battery disposal bins at all of its firehouses and other locations do the same.