So basically 5s4p, I want to lay this thing down on the long side. I’m going to have two of these arrays connected in series with BMS wires connecting to the respective 4parallel cell groups. Is this something that other people do? If not is there a reason they don’t do it this way? Am I gonna have problems with this method?
I might also put the cells in a rhombus shape so that they’re packed more efficiently: https://i.imgur.com/574EBzO.jpg
The design is solid IMO. Keep in mind that you will need good separation between each parallel pack. Fish paper, cardboard, thick paper tape. Also enough nickel strips to handle the current between serial connections. I like to use 3/8" braided copper for serial connections. Stacking up lots of nickel means more more welds/rigidity and places to break with vibration.
Forgot to mention the insulation paper rings for the positive ends of the cells. Very important to add them to a pack for safety
Yep they’re already in my parts list will definitely be using those. When you say separation between parallel packs do you mean the other 5s4p battery or are you referring to something else?
Also, adding the separation materials for safety can make the volume add up quickly, so space might be an issue.
Yes and each for cell parallel pack also needs to be separate from the next one that it’s connected to in series. The entire outer shell of the 18 650 batteries are negative. the shells can break down over time due to vibrations if they rub up next to each other can cause serious shorts and 
Interesting, I haven’t seen anyone bring this up before but yeah it may be a good idea to heat shrink all the four packs.
You don’t need to necessarily use heat shrink, just make sure there is good spacing, and a good barrier between each pack connected in serial. I usually use a couple layers of masking tape, and a little extra hot glue
please do this, parallel groups are likely to short overtime as vibrations damage your pack
plenty of threads to search up and read into 
Yes I said hot glue. Lol. Some people complain about hot glue melting when the batteries get hot, and ruining the spacing and blah blah blah. However, if you have good conduction due to proper amount of nickle or copper, and you use your batteries within their recommended limits, they won’t get hot enough to melt the glue
use 2 short strips of this stuff or non tinned copper braided strip for each of your serial connections.
I’ll add that to my list.
Cool. You won’t be disappointed. The braided copper strip is a little tricky to solder with because it sucks up so much of the Soder.it may be a good idea to practice on an old cell before you add it to your pack, because you obviously want to be quick and efficient when applying heat to the 18650s. Lots of videos out there on how to solder to an 18650 the proper way. Good luck!
