so, as I spoke to both party (yay, I love parties !) I though I would drop some pieces of advice & knowledge here to dissipate the mist & fumes of battery myths
first off, it's indeed very easy to find horrible videos on youtube and elsewhere about accidents with lipos. And also the guy who ruined his BMW passenger seats (we told you it's the most dangerous place in the car). Point is, those are about overcharging (and most of the time, done in purpose or with a really stupid / incorrect charger).
- No the chemistry by itself isn't more dangerous than lipo. Before adding vents on batteries, even alkaline could kill or harm a lot.
The issue is in the mechanical aspect of the battery and in its use.
- Yes li-ion would leak if over charged but they have safety vents which prevents from explosion.
- yes a charger can "go wrong", just like the iphone 4 our tech is trying to fix at work, battery is like a marshmallow which cracked the phone open by pushing the plastic
- lipo hate high temperature more than li-ion due to the lack of thermal isolation with the bag. My spare cellphone lipo battery that I forgot on my desk audio amp (which is probably not more than 30°C) has naturally inflated.
- lipo use a thin plastic bag. The risk of puncture is important in a saber that receive impacts or can be dropped.
So again, it's about the use we do of those and the form factor of the cell. If you open a laptop battery, you'll find more likely a bunch of 18650, not a custom lipo pack in a sealed enclosure. You'll notice also that lipo cells are used a lot on portable devices with little heat and no resistance to opening, there's always a soft cover that can pop out in case of issues. That's part of the regulation to use them.
Situation is totally different with R/C equipment. Be also aware that most lipo packs DO NOT have protection PCBs because... yeah, it's kinda bad to trip it due to low voltage detection when your helicopter is still 30 m in the air. Also because they would reduce performance due to the high current flowing thru the motors.
Some individual SMALL cells (3.7V) have protections, like the ones we use for our portable wifi transmitters at work but again, never enclosed in anything rigid.
So, the form factor combined with the lack of PCB (for multicell packs) and the mechanical weakness makes it a really poor choice even if "it's there and available".