In short, it is overvoltage during charging or overheating during rapid discharging that cause them to ignite. But the main reason is very poor quality, wrong materials and lack of any safety measures to prevent overcharging and overheating.

First let me explain the difference between a cell and a battery pack.
A cell is just that a single battery cell it could be of various chemistry and size.
A battery pack could be a single cell or multicell configuration of cell in parallel or series or both. However, battery packs are required to have a battery management system (BMS or BCM), temperature sensors, enclosures, etc.

Vaping devices are mass produced, and the batteries used are of very poor quality and mostly without any independent third party certification. Also the worse thing for any battery is a short circuit, however, in the vape operation this is exactly what is intentionally done, over and over again. Over a period of time due to continuous introduction of a fault condition (short circuit), the lack of BMS and other reliable safety measures, the cell overheats and enters the state of thermal instability or rundown. This is why they explode and catch on fire. Few years ago, UL published a standard UL8139 specifically for electrical system of e-cigs.
https://ctech.ul.com/en/news-new/ul-8139-electrical-systems-of-electronic-cigarettes/ BTW Most popular cell for vaping is type 18650, which should never be used on its own.

Same applies for hoverboards, except hoverboards use battery packs. When hoverboards started exploding, we were tasked with the evaluation of the batteries and we were shocked by the design and lack of any safety measures. The chargers were also equally bad, never certified and in many cases were counterfeited. They were extremely dangerous, I have seen masking tape used as an insulation!! Keep in mind they were made for a quick sale.

For that reason U.S. Consumer Product Safety Commission (CPSC) requested that a new standard for Hoverboard is developed and in May of 2016 first certified hoverboards by Segway were introduced to the market. The standard is UL2272. Razor, Radio Flyer, Segway are among 50+ manufacturers of safe certified hoverboards.

Batteries are now most counterfeited products in the world. There is a huge demand for replacement batteries that is fueling counterfeiting.

 

Thanks for the scary explanation...I feel even better about not putting one in my bike, especially an uncertified, counterfeit one.
Screw you China.

 

Again keep in mind LiFePO is not the same as Li-Ion! There are few really good companies that make LiFePO batteries, Shorai is one of them but you will need a charger as well.
I have no problem having LiFePo battery in my race bike (weight saving)

 

I like to live on the edge. I vape while riding my hover board, and dressing up like a pirate, but I'm a badass like that. No ragrets,

 

Lead acid batteries explode.

 

How is it that the motorcycle charging system is ok for all types of batteries, but you need a special charger for AGM, and a special charger for Lithium?

 

I had a pinto... Great little car, took it to. Mud bogs where 4 wheelers got stuck I bounced across the top..
Almost want another one! Pop the echo boost motor in it and a screamer

 

It's because people are too stupid to use it. They use regular charges instead of chargers made for lithium batteries.

 

Thatll buff right out

 

Lead acid batteries produce hydrogen as they charge; if the charge rate is not correct and they are not ventilated properly, they can go boom.....I was working for Atlantis Subs when one of the Voyager subs (competitor to Atlantis next door) went boom.