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Question for DIY battery builders

G

GuyG

Solar Enthusiast
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Feb 4, 2023
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I’ve always been a DIY kinda guy; like to tinker with things, especially when it can save me money. So when I saw threads here about building battery banks from cells, I was intrigued. Have read a lot, checked on pricing, but must be missing something.

It looks like 16 cells needed to build a 5 KWH battery would cost me well over $2,000. Add to that a bms, some wiring/cabling, breaker, and maybe a case. But I can buy a 5 kWh unit for under $1,800 that includes everything above, plus a warranty. And places like Sig Solar will throw in a rack/cabinet if you buy several batts.

Someone please help me see what I’m missing in the cost-benefit comparison between buying and building a 5 kWh pack.
 
Building DIY battery's were MUCH more cost effective just a year ago. Not so much any more. You can still save some money, but you need to buy larger capacity cells, and in higher quantities.
 
Everything has gone up in price, but even still, looking at pricing for 105ah cells at 180650batterystore.com isn't that bad. The 280ks would put you over the cost of the 100ah server rack battery, but get you almost 3x the capacity.
 
This forum is oriented toward LifePo4, but Lithium-ion 18650 2nd hand cells are even more cost effective BUT need a lot of DIY free labor to save $. Especially 5 years ago. I'm running about $200/kwh (complete/everything) for my 121kwh (13,000 cell) Powerwall. That's $1000 for 5kwh which is an OK price even today but it has been many, many, many hours of labor.

In addition, to have any chance to get in the same ballpark with LifePo4 charge/discharge cycles one has to run at a very low DODs. My lifetime average DOD over 1,600 cycles to date is 36%.

1678310684003.png

And, to try to answer the question - for me, there was a huge element of FUN to DIY'ing my own powerwall :)
 
Last edited:
Add up the tools, cables, and everything else you need to DIY and your better off just buying a battery IMHO.
 
Wjm1964 said:
Add up the tools, cables, and everything else you need to DIY and your better off just buying a battery IMHO.
Click to expand...
Only tools you would really need is a torque wrench for the bus bar connections and a crimp tool for the balance leads. If you couldn't borrow those from someone, your talking well under $50 for those. Cables would be needed regardless, but you can get them built to size already. Then you're talking about a circuit breaker. Still a whole lot cheaper to DIY for the capacity you get from a server rack battery.

Obviously you can make your pack as complicated or as simply as you want to and that changes your bottom line cost.

Don't get me wrong, I do get the appeal of the server rack battery. You buy the battery and your done.
 
Wjm1964 said:
Add up the tools, cables, and everything else you need to DIY and your better off just buying a battery IMHO.
Click to expand...
IMO Tools are never factored in DIY projects, only consumables going into the project.

Tools will be reused countless other times on future project and another excuse to go shopping that doesn’t involve me waiting for the wife to leave the dressing room.

Cable and crimping high current connectors will be needed if you build a battery or use a server rack, so again that’s a wash.
 
timselectric said:
Each battery I build costs almost $3,000.
280ah cells, JK BMS, breaker, and wiring.
For that I get 14.33 kwh
That math works for me.
Click to expand...
I applaud you for how you've built such a monster system without breaking the bank. I haven't been quite that hands on but I've been plenty hands on to suit me, lol. My math says your way is about $209 per kwh and I can buy the deal from SS including the rack for around $283 per kwh. That's quite a difference but in my case I'm willing to cough up the difference and not mess with the build. Everyone has their own priorities, etc. Of course I'm still gonna buy all the tools because, well, I mean, you GOTTA have tools!

Speaking of which, I finally broke down and ordered a torque wrench because I couldn't find mine and I didn't want to endure more nagging about my redneck armstrong torquing procedures. ?
 
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