Wired has a good article on fires from “hoverboards,” which are essentially very small hands-free electric scooters. Here is an example. Start at about the :30 mark to see how these devices explode, and can easily set a house on fire.

Neither Wired nor other news stories have much constructive advice about how to reduce the chance of fires. As they point out, buying a well-made model is important, but at present there is no way to distinguish the well-made ones from the knock-offs. And most are cheap knock-offs by companies that will be gone in a year.

I have some experience with the underlying cause of these fires,  their Lithium-based batteries, because I use them in radio controlled aircraft. Fires of these batteries are not common, but they happen. Two people in San Diego who I know directly have had major fires. One lost a 2-unit condo, the other a detached workshop. The second one happened to an expert in RC flying!

Here’s the cause: Any lithium-polymer battery that is overcharged, or has a short circuit, will catch on fire. The batteries in our cellphones and computers are very safe because the manufacturers realize this, and provide several levels of protection. Both the battery itself, and the charging circuit, monitor to prevent overcharging. And the battery is designed and manufactured to a high standard of safety. (You could still cause a fire by driving a nail through the battery, or a violent accident, but that is about all.)

In Radio Control flying, we mainly use cheap batteries to save weight. But we use expensive chargers to prevent overcharging, and we follow these rules:

• Never leave a battery alone while it is charging.
• Expect to spend $50 to $100 on a good name-brand charger. Learn to use it properly; they require simple programming for each type of battery.
• Charge on a concrete surface, outside, or in a fire-safe bag. In my case, since I live in a warm climate, I can use all 3.
• Keep a fire extinguisher or a bag/bucket of sand handy. The smoke from even a small fire smells awful, and will stink up a house.
• If the battery begins to swell, treat it as suspicious. If it swells a lot, dispose of it. (Disposal is its own procedure.)
• After any crash, treat the battery as suspect, especially for the first few hours.

I suspect that what has happened to hoverboards is that the makers use cheap chargers that do not protect well against overcharging. The batteries themselves don’t have proper built-in protection circuits. (If you look at a removable notebook or phone battery, the packaging conceals a fair amount of circuitry.) “Many modern batteries incorporate all kinds of safety measures, such as emergency vents, and many products filled with lithium ion batteries have to endure a barrage of drop tests, crush tests and electrical stress tests before they can pass.”

Despite these precautions, battery fires happen. We try to ensure that when they happen, they don’t have serious consequences. I was lucky because early in my RC flying I had a battery start to smoke while being charged. After that, I took the problem seriously. This picture is not mine!