How dangerous are LiPo batteries really?

Last weekend at Galaxycon in Columbus OH I found a vendor that had 3D printed stuff, and he had this mouse droid for sale.  Uses a Traxxas Bandit something (brushless) car and only needed a battery.  For $350 I couldn't pass it up.

But I've only used NiMh like 10 years ago, still have a couple cars (the Wheelie King truck/Jeep will become an offroad mouse droid this winter hopefully).  I stopped by the local hobby shop Monday and bought a battery and charger.  The instructions (& multiple online sites) talk about charging bags, don't leave unattended, only charge on concrete surfaces, etc.

Yeah, I charged the battery for about 15 minutes on my kitchen counter till it said 100%...

Did like one battery 9 years ago go kaboom or something?  Or are they really that sketchy?

 The only LiPo I've had catch fire was in a RC plane that I crashed hard. It burst into flames while I was picking up the wreckage and even covering it with sand didn't extinguish the fire. 

 I charge my LiPos with a smart balancing charger on the concrete shop floor and even then only when I plan to stick around. Like I say I've never had an issue and lithium batteries are used in everything these days so this may be overkill.

The only lipo I had burn up got tossed out of my Rustler VXL and dragged across a parking lot at 40 mph, that was bit exciting but the car was fine. I have smashed a few airplanes and a number of helicopters into the ground (build, crash, fix, crash, repeat lol) without a lipo exploding.

I've also had one battery swell up while charging so Wayslow's recommendations on charging them are good to follow.

The Li-po batteries for my helicopter I charged in one of these. I would leave the lid open for cooling. It should contain the fire well enough to keep it from burning the house down. I also stored them in it in case they decided to burn when in storage. 

LiPo's go thermonuclear when you attempt to shove too much power into them, are too highly charged (above 4.2v per cell) or are discharged too hard. Their bad rap is mostly because of idiots not doing their due diligence, secondary to their poor lifespan at ~500 cycles.

Basically- only charge to full to top-balance cells, so do that to 4.2v (or manufacturers recommendation) every month or so, leave for a few hours, retest voltages to see if any are dropping faster than the others, then use the battery for a little bit so it doesn't stay in that "full" state. Charge it when you're around, and for both safety and longevity only go to 4 volts-4.1v. Do it at room temperature, in something you can isolate and evacuate easily. Finally, don't charge it ultra fast unless you're at some kind of function- slow charge is best.

Back in 2019 my boss and I went to the Battery Show.  One of the most prominent products were cell separators that were supposed to keep one cell from igniting the entire pack.  We looked at each other and said "Glad we us lithium iron phosphate and don't need those".

They have fire bags specifically designed for charging LiPo batteries for a reason. 

I have seen numerous lipos catch on fire.

I used to be really heavily into onroad rc car racing traveling all over the country to race.  Seemed like every other major race had somebody running out of the building to fling a burning / venting battery into the parking lot.

Do you have a Traxxas battery and a Traxxas charger?  They are make it pretty easy to charge the battery safely. If you have something else you want to know how to balance charge it like Girthquake said. We have several  Traxxas Cars and have not had any issues charging them and have crashed them hard without a battery issue

Houses have been burnt to the ground. Yeah, they can be dangerous.

I've got the big boys in an ammo can In the garage, but numerous single cell airplane packs (about the size of a Carefree gum stick) in the basement. One of those decides to commit murder-suicide, there's enough flammable stuff in the hobby room that this house will be an inferno before I get to it.

I think I'm getting another can tomorrow.

The other fact of safety about them, is because their applications tend to be "I NEED every inch of space" they lack a cell/pack level BMS and instead, rely on the charger to do that work for them. BMS are basically failsafes for that entire pack including acting as a fuse, with obvious end results when they aren't used.

Toyman! said:

The Li-po batteries for my helicopter I charged in one of these. I would leave the lid open for cooling. It should contain the fire well enough to keep it from burning the house down. I also stored them in it in case they decided to burn when in storage. 

I like this.  I have a smaller version in the garage left over from Geocache adventures.  I just got it out, still had all the old computer and photography stuff for people to trade.  Gonna clean it up and keep it in my office with the battery inside.