Lipo batteries are extremely dangerous... beware

I love multicopters... I built a couple of them based on the multiwii project. They are fun, affordable and the mostly, you can build them yourself !

RC helicopters and planes (almost) all use Lipo batteries and those are DANGEROUS ! I nearly got my home destroyed by a lipo fire. Look at the video below to see what would have happened if I did not get there in time.

First of all I must say

• I take good care of my batteries
• I use a specific charger (balancing the load between the cells)
• I always charge my batteries in a fireproof bag (which are not that good)

This morning, I was charging one of my cousin's 3S 2200mAh Lipo batteries when the battery started heating and swelling very a lot (inside the fireproof bag). I immediately unplugged the charger and went to the window to put it outside on the sill:

On the red circle above, you can see that the bag was slightly damaged by the heat.

After giving it some time to cool off, I opened the bag to find the battery had "exploded" but did not start to burn:

It may well not look like much but I was about to have a fire in my living room. Here is what would have happened if I came 5 minutes later (scary, isn't it?):

Conclusion... do use these fireproof bags -even if they don't help much- but DO NOT EVER LET YOUR LIPOS CHARGE UNATTENDED