What lights are you interested in?
Are you concerned about the batteries themselves (like safety related) or how the whole electrical system works together? Many responses here are just talking about the batteries, but I think you are taking about the whole system including driver and LEDs, which can be more confusing and complicated.
Here is a starting guide for different driver types.
Yeah I think your right, the 21700 in the Marauder2 are protected although when I opened up my older X7R-Marauder which has inbuilt 4x18650 cells they were pink Samsung 30q’s which U believe are ‘unprotected’. What’s interesting too is a local eBay li-ion seller that just sold high quality cells has been forced by eBay to shut his shop. He was the 1st one here selling li-ion cells through eBay & had been doing it for over 10yrs. So things are changing with regards to how the cells are distributed, not sure if it was a liability issue or not.
Maybe he just needed a pat on the head and reassurance. That is available here, but there is a ‘price’, adult learning required.
At least he had the decency to say good-bye, instead of the one question, never to be heard from again post.
Don't worry ...the more you read the more you'll realize you're not the only idiot on the forum .
take Lightbringer for example :)
I bet Lightbringer will probably see that, though I doubt he'll care. 
Hey!
See, we were not scary enough 
Welcome to BLF CRC 
Maybe Boaz is dressed up as Dr. House and can therefore get away with calling people an idiot. 
A few people on BLF have in my vision earned some privileges over time because they stick to being who they are. Boaz is certainly one of those, and Lightbringer too.
Even the squirl was close to that, come to think of it, but nah, he was annoying. 
The raccoon also comes close, but he's uber annoying... and evil! 
I want to add, that part of the reason to stress battery safety, is the fact that some people just do not think. It should be common sense, that one should not put a lithium ion battery in their pants pocket with their change, so close to important parts of their anatomy. There has been people who did that, and other equally illogical things with batteries. It is stored energy, and stored energy wants to escape the container it is stored in as quickly as possible. Some vendors might peddle weak containers, ignoring the danger in pursuit of the dollar, so avoid these profiteers. Use good batteries from trusted vendors, use common sense, and use batteries suited for the devices they are used for, and it will be fine. If a vendor puts a label saying 9800mah on a 18650 battery, that is a lie, as no 18650 battery exists with such high capacity. If they lie about the capacity, they might lie about discharge rate as well, so do not trust it. Buy quality batteries with a sufficient discharge rate for the device that you are using, and do not mix older or different batteries when more than 1 battery is used. Don’t use any vendor that peddles batteries with mah ratings that are not possible. A battery is not something to sacrifice safety in favor of saving cash. If a deal sounds too good to be true, it likely is not true. Likewise if a vendor claims their light emmits 5 million lumens of light, avoid that vendor.
Hey CRC! Welcome to BLF
I just wanted to let you know that…you don’t need to read all the things in the links
Also, you don’t need to have “extra” knowledge or skills to be into this hobby (I say it by personal experience)! Although your wallet may need to have something inside… 
Knowing more stuff is good, and knowledge is power, but sometimes asking stuff here gives you direct answers for which you don’t need to search the whole web
On a post above you said:
Maybe we can help you on this! Let us know what type of lights are them and if you will give them a specific type of use!
Don’t quit on this, unless you really want, of course
Have fun :partying_face:
There are some dangers involved and you need to be aware of some or most of them. I do believe that everybody should have a multimeter to be able to measure
battery voltage. Even if the light you choose has an onboard charging system I think you should have a way to externally charge the battery and of course spare batteries. At that point you have loose batteries and you need to be aware of the dangers. So that’s why.
I almost forgot the whole Olight angle. Most Olight flashlights use a normal battery that they have modified. So you can sometimes use their batteries in other flashlights without short circuits and you can sometimes use other batteries in their flashlights but they will not charge. That’s a whole other separate class. If you haven’t taken that class do not try to mix and match regular batteries in Olight flashlights or Olight batteries in other flashlights.
Crc- I'm an idiot and im learnin me some stuff. Just stick around here snd keep readin buddy, you'll be fine. Welcome!
When I was a kid I used to dissect Carbon-Zinc batteries, but that was because the larger ones had actual carbon/graphite rods that had all kinds of interesting uses…(to me, anyway)
Yeah it’s a cheap hobby taking things apart. The not so easy part is putting it back! My next project is an old car battery.
Those graphite rods have quite a few uses too. They don’t stick to metal. They don’t contaminate other metals. They stop oxidation. Good metal too have around.
I think you already know but there’s actually lots to harvest out of an old battery. Better that then if it ends up in a landfill. Battery Harvesting
The fact that you are asking these questions shows you have a healthy respect for the dangers of handling Li-ion cells. I think you’ll be fine with any of the lights you mentioned. All you need is some decent cells and a reliable charger.
Stick around and do lots of reading. There’s a wealth of knowledge to pick up from the experienced members here.
I personally have not had good luck with Olight lights, to the point that I won’t buy another. My Javalot has been great, but the 2 batons I had were both glitchy. They never quit on me entirely, but they just weren’t predicable. They both had issues coming on in the right mode and with switching between modes. One of them had onboard charging that did not work consistently.
I don’t think the FW series of lights is for you. The people that got working lights love theirs, but search for any FW thread here and look at the number of people that have huge issues with them. ranging from small glitches to outright dangerous lights.
That said though, anything with a lithium battery can be dangerous if you ignore the precautions you should be taking. They do a good job of making them very safe, but google iPhone fire and you’ll get tons of hits from people with property damage or injury from a phone (iPhone or other) catching on fire. Almost all of them seem to have started though with people not taking proper precautions while charging them.
It’s really like anything else, learn a little bit and take the right precautions and you will be fine. You probably already do it in most areas of your life without realizing.
Think of it like a car. The batteries are like the gas you put in it. 4.2V is a full gas tank, 3.7V (or somewhere around there) is half a tank, and you need to refuel (recharge) when you get down into the lower 3Vs. The current is like the octane rating, higher performance cars need higher octane gas (generally speaking). Brighter lights need batteries that provide more current. And you need to use safety precautions when you refuel. After all, you wouldn’t light a cigarette when you’re filling up your gas tank would you? You already understand all the principles you need to know to use batteries safely.
