@tlfong01: Thanks for bringing up another thing that can potentially go wrong :) When I read the article that you have provided my impression was that when voltage of the cells is quite similar then there shouldn't be any issues. Nevertheless I will have that in mind.

Thanks for the answer. You are right, I've missed the importance of the box, I was focused on what is inside. I wanted 3D print the box for the pack, but not for safety reasons.

In the question 3 I meant something different: There are chargers where you need just to plug balancing cable (i.e.: amazon.com/dp/B08L7VCBXG ) There are some where you need to plug both load cable and balancing cable (i.e. amazon.com/FCONEGY-Battery-Balance-Discharger-Batteries/dp/… ). What is the difference between those two methods?

A note on complexity is also very helpful. Some of these measures may be unnecessary and at best will do nothing, and at worst may create new problems. Thanks for making me aware of this.

Thanks for the reply. I used to say that safety was the number 1 priority, but now that I think about it, that wasn't true. I was actually more along the lines of "I want to build a very safe battery pack myself (educational goal) at a reasonable price". I can build many other things myself that won't blow up in my face, so I can buy an already manufactured battery pack. As for chemistry: I'm not attached to Li-ion at all, if there are any safer ones I'm happy to use them.

@tlfong01: No I'm not EPAC guy, I'm just the guy don't want make set a fire in his house. For EPAC I would have to build significantly larger battery packs, mine will be at most 3S2P.

@KyleB: I dont intend to use LiPo, mainly for safety reasons. I want to use Li-ion.

In the third point I've written that it doesn't matter whether ground is connected to the middle or extreme terminal and you answered to my first question that if ground was switched with the output then no signal would get to the output. Unless I'm missing something those two statements are in contradiction.