Cordless tools have really come a long way in the past few years. I can say that our company has invested a fair share of money into them. From nailers to saws and even compressors, these tools now have the power and battery life to last several hours and it makes our job so much easier without having to run extension cords and fight for power on jobsites with other trades. (Photos 1-5 depict some of the trusty battery-powered tools I use every day.)

If you run tools with batteries, you may have a few different brands like we have. Wouldn’t it be nice if one battery fit all brands? But that’s not the way it is, and you always need to make sure you have extra batteries. So what do you do? Probably the same thing we do: put the charger and the batteries in a tool bag. (Photo 6)

However, we recently learned something about this next generation of portable power the hard way. My son Jason experienced a raging fire in the back of his truck bed. He had batteries from several different manufacturers stored together in his battery bag and had parked his truck in the driveway for the night. Around 2 a.m., Jason and his wife, Ashley, were awoken to the doorbell constantly being rung.

Fortunately, his neighbor across the street had just happened to be outside when they noticed a fire in the bed of Jason’s truck. Jason grabbed his fire extinguisher as the neighbor brought theirs over. By that time, the fire had risen up to about 8 to 10 ft. above the truck bed! Jason and his neighbor worked together to slow the fire with their extinguishers and a water hose, but it was so intense that they were not able to stop it.

Ashley kept telling them both to back away, but when your truck is on fire your natural instincts are to try and extinguish the blaze. What made things even more dangerous was that the fire was situated directly over the gas-fill tube and the truck was backed up to the garage.

Fortunately the fire department showed up and was able to put the fire out. There aren’t any pictures of the fire itself as everyone was in panic mode trying to put it out—but the fire melted the rack system and sprayed-on bed liner, ruined the driver’s side rear window, scorched the tools, and turned the battery bag into a big hunk of melted plastic and exploded batteries. (Photos 7-11)

A couple of the firefighters determined that the cause of the fire was Jason’s lithium-ion batteries that he had stored in his bag. They concluded that it was probably thermal runaway. Being that this was our first experience with a battery catching on fire, I had to see what thermal runaway was all about. I looked on the web and found some good information from Industrial Equipment News (IEN).

It’s important to protect your tools. And that includes the batteries—especially since ... doing so also protects ourselves.

Lithium batteries are popular because they pack a lot of energy. However, under certain conditions they will catch fire because they contain a flammable electrolyte and are kept highly pressurized. (As a side note, this is why airplanes won’t let you fly with lithium-ion batteries in your checked luggage.)

If the batteries have a manufacturing flaw, are damaged, are packed too closely together, are overcharged or are exposed to excessive temperatures, they can overheat. This is what causes thermal runaway—where the increase in temperature causes continuous further increases; it’s basically an uninterrupted feedback loop. So if a single battery begins to overheat, it can cause nearby batteries to overheat and experience thermal runaway as well. The flammable electrolyte within the batteries can also ignite.

We really don’t know exactly what caused the fire. Was it a defective battery? Were the batteries grouped too close? Did two batteries’ leads contact each other? Was it because of different brands in the same bag?

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It’s anybody’s guess. So are we paranoid now about using batteries? No, but we are definitely more aware and may start doing a couple of things differently: such as not keeping all the batteries in one bag, getting a metal toolbox to store some of the batteries, and using plastic covers to protect the terminals. It’s important to protect your tools. And that includes the batteries—especially since we’ve learned that doing so also protects ourselves. (Photo 12)