Electronic – Diy 18650 4s battery pack [How to charge, how to build?]


I'm building a bluetooth portable speaker.
However, I have some questions about building my first 18650 battery pack.
I have 4 pcs of Panasonic unprotected NCR18650B 18650 3.7V 3400mAh.
enter image description here
My goal is to build a 4s 18650 pack with these batteries, and the battery pack must:
– be inside the portable speaker
– Fully protected
– Safe

My question is, how do I design this battery pack?
I have a idea, but want to know if it is a good way to build it?:
enter image description here
I also have some others questions:
During my searches on internet some people use balanced charge, is it necessary to it use in my case? If yes how?
Do I need to use a power adapttor or lithium li-ion battery charger adaptor?

Thanks for your future help

So i recap, if i have correctly understand,
A BMS board is designed for protect the cells against Overcharge, over discharge, over current, short circuit protection, right?
But for protect the batteries pack life, it need to be balance charge right?
Which board can you advice me for protect and balance my batteries pack? (I have Panasonic unprotected NCR18650B 18650 3.7V 3400mAh)
I found a board on aliexpress, what do you think?

enter image description here

Or i have an other idea,
what do you think if i put a balanced charger in the speaker,
does it possible the wires stay always connected to the charger and the speaker circuits?
Does it is necessary to have a bms for protect my batteries because they are original unprotected ?

enter image description here

Another question,
Please, can you advice me a reliable BMWS for protect my batteries pack?
I'am not there to save money, the safety of the pack is my priority.

I checked the existing BMS on the market, but i noticed that Over-discharge Protection is too low compared to my batteries specs.
The common bms on internet cut the current at approximately 2.55 this is too low for my batteries.
Indeed minimum voltage of my batteries is 2.75 V.
So i found a new BMS with balance charge function: link

I have several questions, i made a wiring diagram and i want to know if don't have made mistakes:
enter image description here
However, several questions remain vague in my mind:
The Positive cable and the negative cable are the same cables to charge the battery pack and use it? On the diagram (Output / Input Positive + and Output / Input Negative –)
Can i use the battery pack at the same time as it charging? For me it seems odd to me because I wonder what the intensity and the voltage sent to electric circuit of the bluetooth speaker. On the diagram (Intensity: A?
Voltage Rating: V?)

Those of the adapter or the battery?

Best Answer

That BMS looks identical to one that I've used and it does NOT do balancing or proper charging. Just protecting from over current, over voltage and under voltage - all of which are very important.

You will need to add balance wires and get a balance charger for this battery.

Balance wires are easy - they go exactly where the bms wires go - one to each pos and neg of each cell. The balance charger will have a slot for those wires.

I recommend looking at the IMAX b6 charger because it is the cheapest balance charger I have seen and seems to work reasonably well up to batteries with 6s or less.