4S 26650 LiFePO4 Battery Pack Case

I made a small case to house 4S LiFePO4 to have a carry-around-sized battery in the 12V nominal range. I used salvage A123 26650's. You'll want to print of 2x of the cell holders, arrange the batteries in them, and spot weld the batteries in series, leaving tabs for balance leads. Use a BMS, there's room in front of the batteries for a small one. I used this one: https://www.aliexpress.us/item/2251832666835244.html?spm=a2g0o.order_list.order_list_main.5.b1191802kZDz2S&gatewayAdapt=glo2usa&_randl_shipto=US but there are probably several other 4s bms's out there that would also work

Then the lid has cutouts for a basic voltmeter, a momentary NO switch for the voltmeter's display, and an on/off rocker switch for the battery output. I chose to simply have a hole with main + and - wires leaving the case, and whichever connector you like (I like xt60s). I preferred that to making some sort of case-mounted connector, but feel free to rework it however you'd like. You can use silicone or a rubber washer to make the wires a bit more secure. Insert the components into the lid first, then wire them to the battery. Then you should be able to lower the battery and lid, with everything wired, into the bottom half of the case, and screw it closed.  I have the main rocker switch between P+ and the XT60, and I wired the voltmeter directly to the battery's main B+ and B-, but you could also put it on the P+ and P- if you'd like. Using the momentary switch in between the voltmeter and the battery prevents parasitic drain; just press and hold the switch to see the voltage pop up, then release.  

You'll need:

Momentary switch, round, ½" or 12mm https://www.aliexpress.us/item/3256803329415321.html?spm=a2g0o.productlist.main.7.739eeab7a7Zm2q&algo_pvid=368947c3-7d35-4b8e-a73d-aad3950b7f19&algo_exp_id=368947c3-7d35-4b8e-a73d-aad3950b7f19-3&pdp_ext_f=%7B%22sku_id%22%3A%2212000026135308007%22%7D&pdp_npi=2%40dis%21USD%214.27%212.99%21%21%21%21%21%4021021a7216714066612711947d0720%2112000026135308007%21sea&curPageLogUid=bNZ1zrg0NvMC

Rocker switch, I used something like this https://www.aliexpress.us/item/3256804695113122.html?spm=a2g0o.productlist.main.5.45b1bbL2bbL2AK&algo_pvid=8c399ab9-2215-4196-b6ec-799b5b54d4b6&algo_exp_id=8c399ab9-2215-4196-b6ec-799b5b54d4b6-2&pdp_ext_f=%7B%22sku_id%22%3A%2212000030877311642%22%7D&pdp_npi=2%40dis%21USD%211.72%211.72%21%21%21%21%21%40212278f516714068674335788d0777%2112000030877311642%21sea&curPageLogUid=3f3OVLBjOer8

Voltmeter, most of the cheap ones are all the same size https://www.aliexpress.us/item/3256803736361812.html?spm=a2g0o.productlist.main.1.3114K3m7K3m7CC&algo_pvid=8202e255-b228-4f68-ad92-06dd5ea7b75f&algo_exp_id=8202e255-b228-4f68-ad92-06dd5ea7b75f-0&pdp_ext_f=%7B%22sku_id%22%3A%2212000027473952207%22%7D&pdp_npi=2%40dis%21USD%210.67%210.62%21%21%21%21%21%40211be59e16714069349176574d0725%2112000027473952207%21sea&curPageLogUid=u5jkweoA52XF 

10-24 screws, 2ea

10-24 hex nuts, 2ea

I've attached some links, but honestly, I didn't use those specific links, I made it with parts I had leftover and lying around. I also added lettering to the front of mine to remind myself what cells I used, but didn't use that in the file I uploaded because you may use different cells. Good luck!

I plan on reworking the design to fit 32650's I have leftover from a project, let me know if that's something you'd like. Thanks!