Will generic brand RC car burn my house down?
November 29, 2017 8:13 AM   Subscribe

There are several RC cars on Amazon that come with a USB cable for recharging. If I bought one of those cars for Christmas, will my house burn down?

I'm looking to buy a cheap remote control car. I've seen a few of these things on Amazon.

Like many other cheap ones, it comes with a battery pack and a flimsy USB cable for charging.

- Is that safe?
- The battery looks like 4 AAs wrapped in green plastic. Could I swap the battery pack for some rechargeable AAs?
- Is the battery a standard RC battery? Is there a standard charger I could get for it?
- Might I be able to spend my < £40 on a car of better quality?

Any advice would be welcome. Santa will appreciate it.
posted by popcassady to Technology (4 answers total)
The battery is almost certainly 4 AA cells soldered together and shrink-wrapped. That's very common in RC vehicles. There are many chargers available to charge these packs, and they're usually rated in terms of number of cells (e.g. 4-8, meaning a pack of between 4 and 8 AA cells).

My kids have had numerous RC toys with similar battery packs, and have never had an issue, other than one of the cells occasionally failing, leading to a pack not charging. I've never considered them to be a safety issue. Charge rates on the cheap toys seems to be pretty slow, and I've never noticed any of them ever getting hot during charging.
posted by pipeski at 8:29 AM on November 29, 2017 [1 favorite]

The risk with Li-Ion batteries is thermal runaway usually caused by physical damage or manufacturing defects. A short is caused inside the cell which triggers an exothermic reaction, causing more damage to the cell, causing more heat, etc. A lot of the damage that might cause a battery fire is invisible, buried deep inside the cell, and might not actually cause a fire until days or weeks after the damage was incurred.

That said - the amount of energy in four AA batteries is fairly low compared to the high profile stories in the news. In fact, I'd argue something like this pack is safer than, say, a cell phone battery because it's comprised of four separate cells wrapped together rather than one large cell (this was the argument Elon Musk made about the Tesla battery packs when the Dreamliner fires happened - large cells contain more energy than small cells, and it's difficult for fire to propagate between cells when they're smaller and more distributed). The fact that the battery is removable is also a point in its favor. I wouldn't worry too much about it.

If you want to be extra safe/paranoid with the battery pack, I would recommend storing it unplugged from the charger or the car. I would also not charge it before storing it - again, the more energy in the cells, the greater risk of fire. If it catches on fire (and I would say the risk is pretty low), pour water on it for several minutes to keep it cool and prevent a thermal event. Don't smother it or dump ice on it. If it's on fire and somewhere with a low risk of catching other things on fire (say, in the toy sitting in your driveway), just let it burn out.
posted by backseatpilot at 8:29 AM on November 29, 2017 [2 favorites]

I wouldn't try to replace the battery pack with just some AA's without a lot of investigation. They could be in series (more voltage) or in parallel (more amps) or a mix with each pair in series and the pairs in parallel... And then there's the chemistry/design of the cells, they could be NiMH at ~1.2 volts or Li-Ion of some sort at ~3.7 volts. Best not to mess with it without knowing.

With charging, somewhere between the USB port and the battery is a charging circuit that keeps the batteries from going BOOM when charging. Sometimes the circuit is in the device and the batteries are dumb, sometimes the circuit is in the battery-pack and the device is dumb. Dumb batteries in dumb device == BOOM.

Apart from charging going BOOM, or physical damage/defect causing BOOM, there's still the drain capacity. Your rechargeable cordless drill or your hoverboard, or your cloud blowing vape device, or your Tesla are really figgin' high drain. Your phone, TV remote, average toy are not terribly high drain.

TLDR; there's a lot to think about before you swap that battery pack with some random AA's.

You'll probably be fine. If it's a fun toy, you'll worry more about finding a replacement battery-pack when the original stops taking a charge. Put it on a plate or somewhere away from flammable things when charging, unplug it when it's charged, worry if it gets too hot or the batteries start to swell up.

You'll probably be fine, or your phone is going to explode.
posted by zengargoyle at 4:45 PM on November 29, 2017

They're perfectly safe. You will be fine. If the battery stops holding a charge, you can look at the numbers printed on the battery pack, and then probably also go on Amazon and buy an identical battery pack because these things are produced for this exact purpose and pass consumer electronics checks whereas replacing the battery pack with one that you manufacture yourself having literally no idea what goes on inside of an electronic device might be less safe.
posted by paco758 at 5:00 PM on November 29, 2017

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