The first 2 photos are of a 2020 4Ah battery, that has become a 4,5Ah battery, with new nickel strips, and the last 3 photos are of a 2017 3Ah battery, that was dissasembled, BMS tested and rebuilt into a 5Ah battery with the original nickel strips. It and a 2016 2Ah are the earliest X20V team packs i have, even Parkside claims that its X20V team debuted in 2017.

Hey guys, wanted to get opinion on my custom battery build.
I had a client reach out about needing a battery for an old electric scooter.

The battery had specific requirements as he had old battery bay - it was a tight fit. 330x178mm and about 74.6mm of height to work with, so if the layout looks weird it’s because of the dimensions.

Specs:
- 7S8P - 56x EVE 40P 21700s (25.9V)
- About 32Ah, around 830Wh
- DALY 7S 60A smart BMS

Used 3d modeling and created custom holders for tight spacing to fit the measurements so I also Laser cut the copper busbars myself - modeled the pack in Fusion first, pic is the cut strip next to the CAD. The C ring cutouts are the spot weld lands, one per cell.
External battery level meter, Anderson SB50 output, comes with a 29.4V 4A charger
2 year warranty on the build

Charged $475 all in - design, cells, BMS, meter, connector, charger, assembly and full test cycles. One off custom job, not production work.

Two questions - anything you would change on the build? And was $475 reasonable, or should I have charged more or less?

The cost of cells was ~$220 and the charger, bms, anderson connector, and other misc (fish tape) probably another $80. So call it about $300 in parts, which left maybe $175 for the design work, modeling, cutting the busbars, cell matching, spot welding, assembly and the full test cycles.

The hours I put in definitely don't math out at $175, but it was a one off and I ate some of the learning curve. Curious where you all would have landed on price.

I would spot-weld the negatives. Then connect each positive to a common bar with one resistor for each cell. Then I would come back a day later and measure voltages. Then I would spot weld the positives if the voltages check out.

Hello,

i was wondering if spotwelding nickel stip to batery and then soldering copper strip on top would be the same as in reverse order. I mean copper stip to batery and nickel on top. Asking because i have not powerful spotwelder for copper.

Hi all,

I'm looking for a good spot welder under $50 as my budget is tight. I don't do heavy work, just making some battery packs for my hobby projects. After going through the local shopping platforms, I found some units that match my budget:

●Docreate TK-10B

●AwithZ U3 Pro (5000mAh, 880A - As per the description)

●Fnirsi FS01 (Pen type 2200mAh)

Which one of the above is worth the price? Are there any other alternatives that fit into the above budget?

Thanks all.

I'm building a battery with 140x BAK N21700CG-50 21700 cells 20s7p. Considering its max output of 105A, with a cross sectional width of about 20mm, what thickness of copper should I use? Where can I find a chart for this information? I've looked around but haven't found anything.

I didn't find anything on the internet

This investigation is a fun side project—My main project is building a wooden boat on my channel, JungleRanch, but this battery build is a fun side project…)

I’ve been studying YouTube videos, papers, and earth battery concepts. Combining my engineering background with extensive Q&A with Gemini, I’ve settled on what I believe is the optimal DIY concentric galvanic cell design.

Anyone who have ideas knowledge and want to comment this post?

I have been studying several Youtube videos and other information some about earth batteries and in general galvanic cell.

Latest I have been communication with an AI (Gemini). Through different questions to this AI and combined my own engineering background, I have come a conclusion of the best DIY galvanic cell.

Key Design Conclusions:

A selection of the question to this AI;
- A Copper Zink cell  in moisture soil will decline rather rapid?
- What if using other material like aluminum?
- So if doing that how long time before needed to upgrade or change
- So if using Epsom salt will have better sustainability but less current?
- How thick should the aluminum or zinc folie be?
- Well the inner roll has less area. Wouldn’t it be better to have the zinc sheet as the outer layer?

Together we came to this Key Design Conclusions;

• Metals: Copper (Cathode) and Zinc (Anode) sheet metal provide the best balance of steady voltage and low internal resistance.
• Geometry: Zinc sheet forms the outer cylinder inside the tube wall to maximize anode surface area, reduce internal resistance, and increase sacrificial mass.
• Thickness: Minimum 0.5 mm metal sheet for structural integrity and long service life.
• Dimensions: At least 100 mm in length (preferably longer) to maximize active area.
• Container: 2-inch plastic conduit, PVC drain pipe, or clear vinyl/acrylic tubing with end caps for isolated cell units.
• Electrolyte: Epsom salt ($\text{MgSO}_4$) dissolved in water and held in saturated sand/peat moss to prevent aggressive pitting corrosion.
• Separator: Heavy-duty landscape fabric, felt weatherstripping, or heavy paper towel wrapping between the concentric metal layers.

Expected Lifespan (0.5 mm Zinc + Epsom Salt): 3 to 6 months of steady discharge per cell before anode maintenance or electrolyte replenishment is needed.

Does anyone have long-term test data on Epsom salt cell current density ($\text{mA/cm}^2$), or suggestions for optimizing the concentric spacing? Would love to hear your thoughts!

When I have built a test example I will log logging exact discharge curves using a ZKETECH (灼智) 4-wire electronic load tester connected to PC logging software to track precise voltage decay and capacity

So if you throw it on the charge it will flash but the lights on the battery will won’t flash until like 4 seconds later in a 2+2 flashing pattern, I can’t tell if that means is bricked or something else.

The Bauer 4v screwdrivers from Harbor Freight don't have user-replacable cells, but that didn't stop me from opening one up and soldering in a new battery holder, after doing some internal case modifications and plastic removal. Now I've got a tool that can easily be opened up and the battery replaced, and I'm so happy about that! It's a bit janky-looking but it gives it character. If I get the chance to get a broken one for free or at a huge discount I think I will cut the case into two pieces in an L shape and that way the entire bottom part just comes off with one screw without the massive gap in the case, but for now I'm happy!

Will make new battery 13s3p

Would need 50A countionue And peak 75A

Will t2 pure copper strip of 0.1x10mm be enough for this task?

My spotwelder is very limited!

And what will be recommended for positive/negative terminal off battery??

Because doing dual sandwich layer 0f cooper doesn't weld well comes easily off!

Would soldering 8awg silicone wire top of cooper sandwich positive/negative terminal be enough for handling this high current?

Thank you

Some dude was literally about to throw it into a sidewalk garbage can, luckily I was there to stop him. 13S 5P bike/scooter battery made from FS INR18650A-2500mAh cells and a (smart?) Jiabaida JH22A40330D0 BMS which I cannot find the datasheet for and don’t have any info on except for what’s printed on the heat sink. Does anyone know which app to use for this BMS, and where to look for this BMS’s datasheet other than Google?

Currently I'm testing out various layouts.

I've check trapezoid layout, but currently leaning more towards an electrically superior layout of 14x5 honeycomb, but it leaves me with small margin to play with.

Currently my constrains are the bike frame (outer triangle), I added padding of 10mm (safe margin - inner triangle) and another 3mm margin.

I'm thinking using a 3D printed enclosure.

Do you guys think it is acceptable amount of space left within the triangle? I total margin left from all sides: 15mm (photos attached).

I've been thing super hard and trying to get AI to help me, but it's just giving me stupid advice. I can't find any information on how to design best layout for this kind of pack form. I've spent all day trying to figure it out. Maybe someone with more experience can help me? I would be very thankful, it's been a headache.

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I have some echo powertool batteries that the boards died and got replaced and my boss is letting me have the old batteries. I have 10-30 18650s that are good. is there a cool flashlight or battery bank or something easy? preferably fast charge. preferably bright. would be nice if it was water proof. I dont see any websites besides aliexpress online unless someone knows of someone selling diy kits. thanks

I'm updating my very old 18650's and have a few flashlights, lanterns, and fans that are low current draw and I prefer using protected cells in them. I've purchased some Amprius SA110's for low current draw unprotected applications and am very happy with them, and am looking for similar performance and capacity. I'm looking at Keeppower, XTAR, Fenix, Modlite, and Vapcel N40 PCB, all protected and all 4000mah. Does any one have any experience with any of the current batch of ultra high capacity 18650 protected cells to the extent you can offer a recommendation?

I'm trying to understand when you actually need to use 2 or 3 layers of nickel instead of one.

If I’m using 0.15 x 8mm Ni strip building a pack for around 40 A max, how do I know which parts need double nickel?

I think not every strip is carrying the full current cause it splits in multiple paths.

Do I look how much current goes through each strip ?

And does stacking 2 layers double the current handling, or is it more complicated?

I need to understand the logic behind it instead of adding more nickel everywhere.

Important: I use non sqaure layout of cells.

Instead of waiting aproxamently 30hours for charging these massive LG M50LT cells, with a different 21700 charger, i had this 18650 charger laying around

Made a free calculator for picking battery/capacitor cells against real specs (weight, peak power, cycle life, temp range) — ranks 13 real datasheet-sourced cells instead of generic chemistry averages. Would appreciate feedback from anyone who specs power systems regularly:

https://energy-density-calculator-eta.vercel.app/

https://energy-density-calculator-eta.vercel.app/

This is a 21700 4S pack I bought, with an integrated BMS. I was using it and it became discharged to the point that the device would not turn on. However I was suspicious because I have 2 more of the same unit and they seem to last longer.

So I measured the output and only got about 7.6 volts. There was no sign of damage and the unit is relatively new, so I unwrapped it and found this. It seems like the connection at "B3" is very bad. The actual cell voltages are all about 3-3.1V, except that 4th one which is at 2.9V.

Total voltage is 12.2 - but the output wires are still at 7.6. Have not tried to charge it, but I am concerned about this. Should I be?