Nice project but please, use female xt60 connectors to the battery pack, way safer!

This project should come with a big warning sign.

IMHO, from +6P and up you should always use individual fuses. =>

One defective cell will cause this "25P -gizmo" to blow up or burn your house down!

"18650 cells rated at 4300mAh" Did you get these at NASA or DARPA? :D

Please please add links to the parts, even just a description of them. '18v solar panel' is not enough to replicate this.

Secondly, knowing that inverters will accept either 14-16v (what an alternator would charge at) or 12-24v would lead me to choose either a 4s or 6s battery bank, the wires would carry more at a higher voltage, lower amperage.

The side benefit would be in making the pack shorter but 33% wider, you would suffer less voltage loss due to long nickel strip.

Most of the parts are locally sourced and found lying around so sadly I cannot provide any links :( and the solar panel is just a generic one, nothing special I guess (I'm no expert).

The inverter I use only accept voltage in the range of 10-15V so the battery pack had to be 3s in my case. Also, the dimensions of my pack had to be linear due to the dimensions of the intended storage space. And yes a higher voltage pack would be ideal for less current but in my build due to many constraints this is the result.

You may have to source different parts suited for your needs, even one small deviation from this build could result in a whole different list of parts in your project.

Thanks everyone for the feedback, and it's my fault for not checking my calculations. I've removed the misleading calculation. This is my first project involving this many batteries, so it's bound to have some mistakes. That is why I did not dive much into interconnections between modules. Also, the current measurement unit I used maxed out at 10A. So, if someone following this, use a suitable unit (about 50A).  Again thanks for the feedback.

There is not such thing as a 4300mAh 18650. And even if there was, with a total 15.91Wh per cell, you'd only get 1.193kWh for 75 of them. 

You can buy 3400mAh cells https://www.orbtronic.com/batteries-chargers/panasonic-3400mah-18650-li-ion-battery-cell-ncr18650b That's what the old Tesla's are full of. But that max's out  ~900Wh for 75 cells.

The capacity calculations of this pack are way off. The title is misleading and what's worse, hackaday didn't check any of this and included it on the top of their email newsletter.

I really like the aesthetics of the pack you put together, thanks. Unfortunately there is no such thing as a 4300 mAh 18650 battery. Only in the adverts of Chinesium scammers like Ultrafire, whose batteries actually test out at more like 1500mAh and often less.  IMR and other reputable battery manufacturers make a 4300 mAh battery but it is the mechanically larger 26650 size. The best you can do with an 18650 is around 3400 MAH and those are very pricey. 

Yes, just done the same calculation... please modify the title of the project!

Definately not 3.5KWh....  your calculations mistake Ah (Amp hours) with Wh (Watt hours)

Somehow a nice but protected project since none of the boards are presented or shown.

And therefore sadly not as interesting as it is quite useless this way. Hackaday sadly shows a lot of inaccessable projects that are useless this way. 

Something seems odd about your calculated total capacity of 3,5kWh. First of all, I don't think there are actual (not just wanky marketing) 4,3Ah 18650 cells out there. The highest I've seen so far are 3,6Ah.

But assuming your cells are actually 4,3Ah, and you are using 75 Cells total in a 3s25p configuration, the total capacity sums up as 

3,7V * 4,3Ah * 75 = 15,91Wh * 75 = 1193,25Wh = 3 * 3,7V * 4,3Ah * 25

Yeah, otherwise why not put them in series to a billion volts? doesn't stack :)

a kilowatt hour is still a hefty amount of charge, though.

1 kWh ist still a lot of charge, yes. Although I suspect it's more in the region of 400-500 Wh as those are likely just 2Ah cells.

The packaging is nice though, been looking forward to building something like this myself for some time now.