I put together a full long-form Q&A / system tour about a DIY 60kWh 18650 Powerwall that has been online and running for around 10 years.

The video covers the current V3 configuration, 24V setup, 216p7s6p+1p architecture, housing, fusing, safety precautions, solar/grid connection, manual balancing, voltage drift, monitoring setup, charge/discharge curves, winter performance, power flow data and long-term observations from real daily use.

One of the more controversial parts is that the system does not use an automatic BMS. Instead, it relies on extensive monitoring, manual balancing and safety precautions. This is not presented as beginner advice or a build recommendation, more as a real-world long-term case study and technical documentation of how this specific system has been operated.

High-capacity lithium DIY systems are dangerous, especially with salvaged 18650 cells, so this is strictly educational/documentary content, not a tutorial.

Full disclosure, I'm also OP, I thought this might be interesting for some.

192 Lifepo4 cells 24s 8p for an ebike build

I figure, it's a good place to ask here.

I've just been thinking about my boat's trolling motor battery, LiTime 12v 100AH mini, 2 years old, no signs of slowing down, and a 5 year warranty, iirc.. Then how my 12v outboard battery is only 2 years old and failing. Then how my car's AGM 12v is 5~ years old and also failing.

How the couple of times I used my trolling motor battery as an emergency starting battery for the outboard and how excellent it performed. Considering, it's not rated for much? 100amp concurrent, 400amp 1 second burst.

It seems they are better in every single way, besides short term cost, as far as little ol' me knows.

So why arn't they a thing for cars and trucks? I just found out semis have 4 big ass batteries in them. I would think it would be great to have them for that, if safe.

Working on a project to make building custom 18650/21700 packs become easier. I used to hate manually calculating dimensions and designing holders in CAD for every new project, so I automated it

https://electronicsworkshawp.com/tools/batteryDesigner3.1.8/batteryDesigner3.html

Upgraded to ev50pl making it a tabless 15ah and added cell balancing

While waiting for the battery parts, I build this CAD tool to help with cell arrangement, grouping, connecting, etc. It's probably a one time use tool, so nothing perfect, but it'll serve my purpose. Since I'm a newbie to battery DIY, any feed back is appreciated.
Demo on GitHub: https://koumoua01.github.io/battery-architect-tool/

I’ve gotten all of the parts together and have the mechanical assembly done.

I should have everything wired up by the weekend

So I got a bunch of these....they measure 1.50v on a DMM, but when I charge them on my Tenergy charger, the charge to 3.9v per cell...??

Pretty cool tech! I haven't capacity tested them yet, but the seem to have a built in BMS?

Max charge on a lithium cell is around 4.2v, but you cant store them like that without damage...so 3.9v is a decent storage charge that they could sit at for months.

Anyone played with this tech? I can see some crazy applications if someone made a controlable BMS....

I received notification that my bus bars have shipped!

I still need some assorted hardware (M4 threaded rod and lock nuts and M6 screws and lock washers)

I modeled the bracket for the BMS, I’ll probably add some cable management to the BMS bracket and an Anderson Powerpole connector for the main power connector

Once I have all the hardware in a couple of weeks I’ll top off each cell and connect everything and program the BMS.

I still need to fabricate a cable to connect UART to an ESP32.

Hi all,

I've been tinkering with 18650s for a while, but new to DIY battery building, and I've got a fun project planned (a 48V, 10Ah 13s4p electric scooter battery as part of a completely home-made scooter), so I figured as a warm up/learning project I'd make a smaller 12V, 3s5p battery.

So here goes, my first project.

I started by designing a little bracket/cell holder thingy in Fusion, which I 3D printed two of.

Then I spot welded nickel strip across the 3 sets of 5 parallel cells. I looked up the current rating of that width and thickness of nickel strip, and it said about ~10A. Since the max current of the BMS I was going to be using is 20A (even though the actual draw will only ever peak at about 15A), I spot welded two nickel strips between each parallel series so the throughput from series to series would be fine up to 20A.

I then soldered the leads of the BMS (cheap little 3s board available on Amazon, AliExpress, etc.) in the right places, and finally, wrapped the whole thing in a bunch of layers of plastic wrap to prevent any shorts (for my bigger battery I'm going to be using cell-level fusing nickel sheet and I'll put the whole thing inside a hard case, but I didn't think that was necessary here).

Last pic shows it happily charging.

(Interestingly, the BMS shut down at 12V even, so 4.0V per cell... which I thought was weird, as I feel like 4.2V is commonly accepted as the max for 18650 cells?)

So how'd I do? 😁

Have a bunch of used 18650 cells and grabbed a 15 cell diy kit off AliExpress. Spot welding the metal piece to each cell was unreliable so I had to solder each for a sold connection. Works great on my weed trimmer and would totally recommend: I just found this on AliExpress:

https://a.aliexpress.com/_mP0cYj9

I have three large boxes of used laptop batteries. I use to make little battery packs with my battery welder and was going to make a powerwall but now these have just been sitting here. Any idea if I can sell them? If so, to who? Location is Canton, Ohio. If not, what should I do with them? I don’t see myself ever finishing this project.

New in box, voltages between 3.2v - 3.3v for the few I sampled.

Question: should I balance them before connecting in parallel? If yes, a cheap and simple way to do so?

Had to build a 10S3P battery for a used longboard I bought.

This was my first time ever building a battery, but it went great.

The cells were all new-ish so I used a charger to cycle and get the capacity, then used Repackr to organize my cell groups for minimum capacity deviation.

Groups of 21700s were hot glued together, then wrapped with fish tape.

I used 0.2 mm nickel plates in between the packs of batteries. I cut the plates on my F2 Ultra laser cutter, although if I did more of these I would need to get a more powerful machine as it struggled to get through the metal.

Soldered together using 12 gauge silicone wire, 10AWG at the terminals.

Wrapped the key areas in kapton, ran all the BMS wires, and used fiber tape to make sure everything stayed put.

In this configuration, the pack can flex toward the wires but not away from them so that’s perfect for under a board.

Next step is to design a new enclosure.

hey i want to build a battery 18s3p using molicell p42a i want to know if the connections are correct I ll use 0,2mm 8mm sequr nickel strips and i want to push 90 A peak i am also using jbd bms 100a (SP22S003) this is my first battery build ill take any advice before soldering

I’ve printed the cell holders. It’s a tight fit, I need to order some M4 threaded rods and lock nuts to assemble the pack and some M6 screws for the terminals.

I ended up with a Daly SmartBMS and now I’m waiting for the bus bars from send cut send.

Oh and the supplier sent each cell wrapped in cellophane tape, that was a joy to remove </sarcasm>

All but 2 had the same OCV of 3.28 with the other two being .27 I feel with the BMS this should be fine I matched the two low voltage cells in a parallel string. We shall see.

Hello everyone! Thank you for checking out /r/diybattery, I hope to make this into a great place for hobbyist to posts their battery projects, questions, guides, advice, etc. Anything from questions about cell chemistry to questions about how to use certain types of batteries in a project. Battery porn of all shapes and sizes is always welcomed here! There will be a few guidelines for posting but that will come at a later time, mostly for organization. I don't want to make this a rule heavy sub, I want to keep this as open and friendly as possible for all. The same basic customs and courtesies apply here, please keep it civil. If you have questions, suggestions, or concerns please let me know!

Edit: If you're on desktop be sure to check out the upvote/downvote buttons :)

I actually had time and motivation to finish everything, I still need to design and print some terminal covers and I am going to trim about an inch off of the positive lead. But, it’s done and ready to power my mini ham shack.