Unfortunately the hotrod flashlight development started here on BLF (about 10 years ago), where we love diving into the details, also of batteries. It led to the consensus that you are supposed to know about battery safety if you are going for a hotrod, or else you are an idiot. The first hotrods were made by hobbyists on BLF (and a few at CPF and TLF) and were completely unsafe, but when actual chinese flashlight manufacturers picked up making hotrods, battery safety was still not priority for them because they were targeted at hobbyists anyway, who are aware of li-ion battery safety.
But nowadays, some higher-end manufacturers (like Olight) do attempt to make their flashlights both high-performing and idiot-proof.
I’m wondering about something similar actually. Has anyone here actually dissected a battery up till the oozy chemical sludge part? What color is it? Is it like peanut butter? Does it burn skin? I don’t see many post from people operating on the battery?
Would be nice to see the parts and chemicals in there. Just need googles, gloves and tools. This way one can see the actual item powering all our fancy flashlights. Yes…battery sludge is your friend! 
Cool! Tell you the truth, I’ve seen and know very little about inside battery…until now.
Woah never knew it has paper wrapping in em. Always thought of them like toothpaste tube. Just paste and couple of metal piece. Hmmm maybe I’ll open one up this weekend! 
Watch this episode of Nova:
From vigorous venting to watching an 18650 manufactured, it’s pretty interesting. So are the youtube videos.
Nice! And from PBS too. They always have awesome shows!
Easy to learn, Easy to outgrow. The hobby can be as much or as little as you want it to be.
Helping a budding enthusiast is never a waste of time.
"Whether you believe you can or you can't, you're right."
Henry Ford
And, it's not over your head if you just wade around in the shallows. Lots of good stuff there. One of the worst mistakes is to be your own limiting factor.
slmjim
You say it’s not safe to keep batteries inside a light long term & refer to your WT-90 as it has 3x21700 high discharge cells. Does that then mean my Olight Marauder-II is a ticking time bomb? It too has inbuilt 3x21700 cells. What about laptops, phones battery packs for tools etc?
I think people love to think their hobbies are ‘dangerous’. I think quality flashlights and quality cells are pretty safe these days if you don’t do anything majorly stupid.
But on a larger scale, lithium batteries can be quite dangerous. I heard when a Tesla’s on fire, it takes at least 2 hours to put it out! It also has to be submerged in water after the fires out for another few hours! 
What?? Are you serious???
Just because you are overwhelmed as a self professed beginner DOES NOT mean you can’t learn simple basics.
You can learn them QUICKLY…. IF YOU WANT TO.
That part is up to you.
Don’t give up so quickly.
Ask questions, most people will be glad to answer & help you with anything.
You can decide how deep you wish to delve into the hobby.
But the basics are really no big deal.
Hang in there…. 
Welcome to the forum! Lights are pretty cool these days aren't they!
Don't feel overwhelmed. While the details of flashlights can actually get pretty technically complex, you can learn as much or as little of all that as you want to, and you really don't have to know a ton to enjoy the lights or the hobby.
The biggest thing is the power source, yes, and while accidents are possible I wouldn't rate it as necessarily an extra-high risk. I think it's less so than what we see these days with laptops and phones and larger devices that use multi-cell battery packs like e-bikes and scooters such (and a little with R/C cars and drones, etc). The lithium ion cells we use just need a little respect and a little understanding - a little more so if you pick lights that use multiple batteries instead of singles. The old (and still somewhat popular) CR123 small lithium metal batteries are considerably more dangerous if something goes wrong but the lithium ion that we typically use poses a lot less risk. Still must be respected, though.
Basically we just have a lot more energy packed more densely into a small package than we do with alkalines or NiCd/NiMH rechargeable cells. A lot of people aren't aware of it, but even little 1.5 volt silver oxide watch batteries can present a decent risk of fire, too, but they don't pack a lot of punch. So...just being aware of polarity when you put batteries into a light does become more important maybe (especially if you buy a light that doesn't have polarity protection). If you make an oops, chances are that nothing bad will happen, or maybe it'll just ruin the components in the light and kill it, but it's possible that a bad situation with the battery can occur.
And next comes choosing a well-made and reliable charger. That's easy and not terribly expensive, but it's important just as it is with other electronics.
And then, in operation, trying not to discharge the cells tooooo deeply into an area of "overdischarge." That generally just kills a cell or reduces its lifespan/energy but it can also present some risks of fire or venting pressure in some situations. Something to be aware of but you don't need to be afraid of it, and you can read more about all that when you feel like it. Some lights have low-voltage cutoff where the light will quit before a cell can be discharged so far, and that's a smart feature to look for, but if you don't mind the slight mental effort involved in staying aware of battery run time and such, it's not a necessity. Most of us notice a drop in performance and will recharge the batteries long before they reach low voltage states anyway. It's just a different way of thinking and awareness than we're used to with throwaway primary batteries. With alkalines and other lower-energy batteries, they just quietly die and maybe leak & corrode your flashlight metal, but they have little safety risk (and of course far less potential for brighter lights).
Have a read through some of the wiki articles made years ago. Some good stuff there and it's easily digestible, although a bit dated and not so updated. Also open up all the subforums on this site and glance at the stickied posts at the top - some already shared here for you but there are lots that are worth reading even if they're ten years old and they'll help you understand quickly. Most of this isn't so hard really until you want to start replacing your own emitters and learn about the electronics of drivers. A lot of people never go down those roads and that's perfectly fine! And some people don't learn about the techy things until they've enjoyed flashlights for several years when they finally spark an interest there.
Wiki: https://flashlightwiki.com/Main_Page
Not at all. Considering how many damnfools buy 10,000,000lm lights with 9990mAH 18650s, and manage to stay off the evening news, it’s nothing inherently “unsafe” anymore than buying a car with 10-15gal of highly flammable liquid is.
Just use common sense like not sticking the filler-spout into the gas-tank with a lit cigarette dangling out of your mouth, and you should be okay with a car. Don’t leave a Li cell in a light and store it in your car in summer when temps can hit 160°, and you should be okay, too.
Most lights that have on-board charging don’t do stoopit things like overcharging, but it’s nice to check anyway. Ie, charge it ’til the light turns green, pull the cell and immediately measure it to make sure it’s not over 4.20V. Next charging, let it sit overnight and repeat the measurement to make sure it still doesn’t keep charging after it’s ostensibly finished.
Do that, and you’ll be ahead of the game and doing more than probably 99% of all owners of Li-powered lights.
“Do, or do not. There is no try.”
— Yoda
That olight has protected batteries!!! Most multi-cell battery flashlights require the use of protected cells, and from what I understand laptops have protection circuits on each cell too. The WildTrail carriage will not accept protected cells, so yes, if the light will be stored for an extended period, remove the cells for greatest safety. If not, and one cell has an internal short it can do bad things even if off. As far as I know…almost every Olight uses protected cells….even most single cell lights they sell are protected.
Personally I don’t think you need to know a lot about batteries to buy just about any light you want. If you aren’t what you need you can post here or on r/flashlight and someone is sure to help you very quickly.
CRC…. Here are a couple of links that should help you understand some basics (& more) about batteries, LiIon especially.
Take your time & read them, if you have questions please ask. Help is available.
Honestly… it IS NOT all that complicated. 
…….
Lithium-ion battery safety 101
Read intro here at Battery U.
- Battery University
https://batteryuniversity.co
START HERE on Battery University
- Part One: Basics You Should Know
BU-001: Sharing Battery Knowledge - Battery University
We should have made sure that fish was in the boat prior to scaring him off. He might have been a future flashaholic. At least let him have the thrill of shining a light in someones window a mile and a half away first. Then he would be hooked.
We were not that scary were we? 