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Question for DIY battery builders

Something no one mentions is asking a vendor if they have "salvaged cells" from battery returns. Lots of batteries get returned because of a faulty BMS, maybe a bad cell or cosmetic blemishes that a buyer won't accept. Another opportunity is cells that have been sitting a long time not selling.

My first DIY project was a third, some 202ah cells that had scratches you could hardly notice but none the less made them "undesirable" to sell and maintain a vendor's reputation
($800) - $50 each for 16 cells with free shipping
($250) - (2) JBD 8s BSM @$125
($72) - 4 sets of "Y" connectors for the BMSs @$18
($1122) = (2) 24v, 200ah batteries (9600wh)

Second project was made from salvaged SOK 206ah cells
same cost as the above

Throw in the cost of the bench power supply (under $60)
Bus bars - Got a deal on some "unfinished/rough" bus bars ($30)
$2330 for 19,200wh

Of course there's no warrantee/guarantee but I found the cells to be good as new, actually capacity tested above stated ah
I won't mention the vendor, he asked me not to tell in order not to be overwhelmed with inquiries.
Bottom line, if you don't ask you'll never know what might be available

Disclaimer: I only asked one vendor and got lucky. Who knows what response I may have gotten from others
 
EastTexCowboy said:
I applaud you for how you've built such a monster system without breaking the bank
Click to expand...
I have been "building" my system for about two years, give or take. Basically save up some $$$, make a purchase, repeat...

It would have been nice to have done it all at once, but life's realities kick in. You know food, gas, shelter, those pesky things that eat up the budget.
 
EastTexCowboy said:
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. ?
Click to expand...
Torque it 'till it breaks and back off 1/4 turn, perfect torque every time. ?

@GuyG if you're a DIY kinda guy, build your own. Great advice here already.
Shop around for cells with the best cost per Wh, it was 230ah for me.
Another big plus for me was learning and understanding how it works.... If a cell goes bad I can easily swap it out with a spare (yes, order 1 or 2 more than you need for your battery; who knows if you'll be able to get the same ones in a year or so...)
 
GuyG said:
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.
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Because it doesn't look pretty like this?
Battery bank.jpg

It will be a shame putting the doors on it and closing it up.

Anyway, as for cost. https://diysolarforum.com/threads/a...ut-ahead-going-full-offgrid.53943/post-701875

Now take the EG4-LL and use the same cycle count of 6000 cycles, and 5.12 Kwh and 90% capacity. Comes to $1700 plus shipping and tax comes to $2006.10 to my door.

5.12Kwh x .90= 4.6Kwh

$2006.10 divided by 4.6Kwh = $436.11 per Kwh

$436.11 divided by 6000 =$0.07268 per Kwh over the expected life cycle of the battery

My bank was $0.0264 per Kwh over the expected life cycle of the battery. The cost of the EG4-LL is 2.75 times the cost per Kwh for the DIY bank I have.

If you went to the one grocery store and they had 10lbs of sugar at 2.75 times the price of 10 lbs of sugar at another grocery store, which one would buy it from?

Edit: forgot the 30% tax credit on the EG4-LL, that would be $0.07268 x .30=$0.0218 so it is $0.05088 for the EG4. Not quite 200% over the cost of my DIY.
 
Last edited:
Zwy said:
Because it doesn't look pretty like this?
View attachment 138762

It will be a shame putting the doors on it and closing it up.

Anyway, as for cost. https://diysolarforum.com/threads/a...ut-ahead-going-full-offgrid.53943/post-701875

Now take the EG4-LL and use the same cycle count of 6000 cycles, and 5.12 Kwh and 90% capacity. Comes to $1700 plus shipping and tax comes to $2006.10 to my door.

5.12Kwh x .90= 4.6Kwh

$2006.10 divided by 4.6Kwh = $436.11 per Kwh

$436.11 divided by 6000 =$0.07268 per Kwh over the expected life cycle of the battery

My bank was $0.0264 per Kwh over the expected life cycle of the battery. The cost of the EG4-LL is 2.75 times the cost per Kwh for the DIY bank I have.

If you went to the one grocery store and they had 10lbs of sugar at 2.75 times the price of 10 lbs of sugar at another grocery store, which one would buy it from?
Click to expand...
Every time I see that picture I get a little jealous, ambitious and eager to order more cells. Very nice work.
I've been keeping my eye out for scrap cabinets at work, my table barely has room for another 11kwh.
 

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I just added another 64 LFP Cells to my system to make a total of 128 LFP Cells. They are 280 AH Cells. I purchased them from Docan Power. All the Cells were pristine in appearance and the voltages were all within 3.304-3.306 volts except for one cell which was low at 3.256 volts. The cost was $8736 for 64 Cells including shipping. I do not have the equipment to test the cells so I just put them all in service and then top balance them while they are in service with a charger and a light bulb.

It does take a bit of work to do the work yourself but I think it has some advantages as well.

1- If one cell needs to be replaced then it is easy to do.
2- If one cell needs to be charged or discharged to balance the pack it is easy to do
3- If the BMS fails it can be replaced free of charge (Overkill Solar)
4- It is cheaper than constructed packs
5- You learn a lot by doing it yourself
 

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I went DIY partially for cost, and to a significant degree because I could buy a few extra cells (went with four extra per 32 because I could make a 12V pack with whatever remained as long as one wasn't completely dead) and know that I could fix it. Shipping lithium batteries to where I am is very difficult, so repairable is high on my list of values. Even as it was, I had to arrange a freight forwarder to actually get my cells to me. Given logistics, if push comes to shove, I'd rather be able to scrap a cell, take a small loss there, and get my system back up.
 
Thanks for all the responses. Good points.

I was trying to compare apples to apples, and the over-the-counter apples were all in the range of 100ah, so that’s what I was thinking of. Think I made some basic mistakes in my math, because after going back to my scratchpad, I can’t figure out how I got a materials cost in excess of $2,000 for a 100ah rack of batteries; would prolly be closer to the $1,500-$1,800 range.

But yeah, there’s a big economy of scale by building a battery out of 280 or 304 cells: cheaper cost per ah of cells, only one bms, only one set of cables, etc.

So I’ll be looking at the options for building a couple of 14kwh batteries for the system I’m working up.

Thanks again for all the responses. Good stuff.
 
Building a battery pack sounds much more fun than a grid tie solar!
Do you have wiring diagram, or something that can get me started?

What size of battery pack can I build with 100 18650s and a single 455W panel? I’d like to build a small system just for the fun part and may be to charge some garage tools!


Thanks
 
Cost is one thing. Control is the other: I know how my system works, I can swap out a BMS if needed, if a cell breaks, I can swap it out.
Never mind that those rack batteries aren't available here (and generally weren't available at all when I built my first set of batteries). I also needed an insulated enclosure and heating, which means if I had rack batteries I'd still have to build something around it.

Also, as others implied or stated, it's fun :)
 
Solarisium said:
Building a battery pack sounds much more fun than a grid tie solar!
Do you have wiring diagram, or something that can get me started?

What size of battery pack can I build with 100 18650s and a single 455W panel? I’d like to build a small system just for the fun part and may be to charge some garage tools!


Thanks
Click to expand...
Building batteries with 18650 cells is a lot of work.
Most people use prismatic cells, now. Since the cost has dropped dramatically.
 
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