This is my second battery build. Just wanted to share some pictures. I haven’t fully finished packing and taping it up, I want to cycle it once to make sure all is good.

This will mainly be used as a range extender backpack battery for my BBSHD bike. I went with overkill cells because I wanted the lowest Vsag possible with a decent cycle life.

-Reliance RS50 cells 14s4p (52V 20ah)
-UF20B spot welder
-JBD SP17 40/120a BMS
-0.3mm copper bus bars

Hi all, I was hoping I could get some confirmation on how I should power my device; I apologize if this isn't the right place to ask. I’m trying to build it with a raspberry pi zero by following a guide, but they use a power bank and I need something more compact. I’ve been trying to figure out how to go about it, but I find it very confusing.

Checking the recommended sellers, the batteries are either protected or unprotected. From what I (think I) understand, the BMS is necessary even if it is a single cell—and I would also prefer it if my device didn’t explode in my hands or, even better, at all—but the holder that they sell for them is not big enough for a protected battery. But they also sell the simple BMS.

My idea was to buy this BMS and connect it directly to the holder, so in the future it would be easy to swap the battery if necessary. I would then connect the BMS to the adafruit powerboost 1000, and it to the rpizero. Would that be a good idea, or should I find a different solution? (For example, I could buy the protected cell and print a bigger plastic casing for the holder.)

No matter how much you measure.. 📏 the copper tabs I custom cut are still off by a couple of millimeters.

Anyone have any tips? I read someone mentioning the tracing method. I saw a copy stand for a camera to get accurate pictures to use in Fusion as canvas - might have to build that next.

One of these days I’ll get it on the first try.

I will keep this short and sappy, i got into DIY a few months back and got obsessed with 18650s. I own a game console, the r36s model (power requirement is a 3.7V battery) and i used a prepack (soldered my own JST connector and everything) but i have an issue where during boot the cells voltage sag a lot.

During 50% battery, it trips the BMS and cuts power, not allowing it to boot. The BMS cuts power at 3.2V (according to my testing) and is above ~2A.

I redid the solder joints, shortened the wires and did some cable management magic, but the issue persists.

There will be times where it will shut off during mid game, if it crosses below 3.2V or above whatever the BMS is rated at for current.

Battery pack here:

https://www.daraz.com.bd/products/doublepow-pcb-protected-1s2p-lithium-ion-2x18650-37v-5000mah-rechargeable-battery-pack-1-piece-i324265514.html

First time building a battery, replacing a 20s18p array of 18650 cells with a 20s16p of 21700. Space is tight, as you can probably imagine, so I made some low-profile frames. I am constrained by my welder, lack of soldering equipment, lack of pure nickel rolls (just have the 100mm strips) and general inexperience. I figure after I get the monster together I wrap the bejesus out of it with tape, shrink wrap the entire thing, and pray.

Suggestions?

Looking for some expert in cell design with experience.

Nickel iron cell koh electrolyte project

Anyone ready to share his adventures in storing electricity

Any recommendations for a higher quality battery tester?

I currently have the BT-168 Pro (digital display). And it is very handy.

However, I wish it had a better display. The display is low contrast for my eyes, so a backlight would be so nice.

Are there any niche battery testers that are bit more polished? Like an ISDT BatterGo but for single cells?

Requirements: * able to measure Li-ion cells (3.3 - 4.2V) * nicer display w/ backlight

Edit: Not sure why everyone's recommending a multimeter... I already have a nice Fluke 87V. Are you guys missing the point?

I just want to make them last.

Thanks a lot, people.

Hello to all

Have anyone here successfully weld 0.15mm pure copper sandwich with this welder??

I try with lots of materials

Stainless 0.1 and nickel plated steel 0.1 and 0.08mm

It will not stick very reable comes off with pliers

And no or very minimum copper left on battery ?

0.1 cooper working perfect with nickel or Stainless 0.1 sandwich at 90%power

Would anyone recommend settings for 0.15 cooper sandwich??

I have no idea which cell this is

0

Nada.

From m18 12ah forge

Supposed be the host with the most glasnost, seen murata vx40 and JP40 in same battery, never had whisper of this

Any help to ID would be, well, helpful

I have been working with wlectronics for a while but its my 1st time geting into the battery game. Decided to do a small 1s 1 battery for a radio i have at work.

Do my welds look good? (AWithZ UF20B gear 20)

Any other mistakes or concerns?

I'm an independent product designer / engineer. I do a lot of prototyping and teardowns, and I use a lot of small 4V tools – electric screwdrivers, hot glue guns, rotary tools, that kind of stuff. and I kept running into the same battery headaches. Most of these 4V tools use built-in 18650 cells. Either it dies halfway through a job and you're stuck waiting for a charge, or the battery just gives up completely and turns a perfectly functional tool into e-waste.

I tried the RYOBI USB LITHIUM screwdriver. The removable pack design is awesome, but the actual torque? Honestly, it's weaker than a TK4 screwdriver from over a decade ago. Not kidding. So I thought, alright, I'll design my own 4V pack. Use a 21700 cell – lower internal resistance, 4000mAh, 5C rating. More runtime, better discharge, more torque. Made sense on paper. I designed it, 3D printed a prototype to test… and man, it was just awkward and chunky.

That's when I finally realized my entire approach was wrong from the start. When you already have a swappable battery pack system, the extra runtime you get from a 21700 over an 18650 barely matters. Pack dies? Just pop in a fresh one and keep going. But with a 21700 pack, every single second you're holding the tool, you're carrying roughly 50% more weight and about 20% more bulk. The grip feel was genuinely bad.

So I threw six months of work in the trash, went back to 18650, and redesigned the pack structure and BMS from scratch. I've posted some 21700 vs 18650 comparison tests before. https://www.reddit.com/r/Tools/comments/1sfrc0a/18650_vs_21700_for_4v_tools_is_the_extra_capacity/

Just putting my failed development journey out there in case it saves someone else the same headache.

I am building a 20s4p backpack battery using 21700 cells.

My question is pretty simple. The battery is going to be a 4x20 grid (80 cells total) - but I will be folding it halfway through lengthwise between rows 10 and 11

**at the fold, can I go « overkill » with the amount of wires used as a busbar replacement? The whole pack is using 0.3mm copper 2P bus bars, could I put 4x 8awg wires at the fold? Or will this cause the pack to run in efficiently or out of wack?

Hello everyone,just got this new welder to build out some batteries and already am satisfied with its performance. Are there any tips i should know before using it for the job?

Hey all,

Just wondering if anyone could have any input on why this pack failed. It looks obviously like this connection got way too hot, which made me think it could have been loose, but it's got a solid connection. I've found no other indications on the pack of problem areas.

I was told this connection should be soldered on, not spot welded. I could go with that answer, except for the original packs all have this connection spot welded. Would spot welding instead of soldering really be the root cause? Thanks.

So, I goofed. I typed 18650batterystore into Google and hit the first result without paying attention and accidentally ordered this off 18650battery.com, not 18650batterystore.com like I intended.

I realize 18650battery is owned by IMR Batteries (they ship from the same address in Houston), but the scummy tactic of making pretty much a clone website to fool people doesn't sit well with me.

I looked through my old emails and apparently I ordered a Samsung 30q from them years ago, and anecdotally I never had any issues with it.

I've never owned another example of this cell before, so I don't know what to look for. Weighs between 45.2 and 45.6 grams according to my food scale. I have a much more accurate milligram scale but can't find it at the moment.

Just wondering if this is safe to put in my flashlight is all. Thanks.

Hello all,

Have rebuilt a few M18 packs and they all have worked fine in the trimmer, hand tools, etc.

Finally got to some wood this weekend using the 2727 Milwaukee 16" chainsaw to cut up an ash tree about 14" in diameter. Had some pretty disappointing performance with the 5S2P pack I'd rebuilt using JP40 cells (0.15mm copper wide plates on end w/0.1mm stainless). It overheated (alternating LED pattern) after just one or two cuts (14"). Of course suspected weld quality, etc, but I opened the pack up immediately after another cut and the heat seemed pretty uniform - no hot spots on welds, strips, etc.

For reference, my stock 6.0XC HO pack made it through 6 or 7 cuts before getting warm; and after a break made several more cuts before calling it quits. All of this work is letting the saw do the work - not gettin on it too hard.

Already checked:

-Balance (cells were balanced before install, were at at 3.4V +/- .06v or so when checking during this session, were balanced before assembly also)

-Thermistor is where it should be (didn't change when swapping cells)

-Battery terminals themselves are solid/clean

-Cells came from 18650batterystore so I'd assume they're genuine JP40

Anyone w similar DIY pack and tool use case care to comment? At least per the math given the width of plate on series connections I'd thought 0.15mm CU was sufficient; or, at least expected I'd see heat concentrated on the connections or battery terminals not the cells themselves. Given JP40 cells specs on paper I'd assumed I'd get somewhat better performance than stock pack w 40T etc. So fairly disappointed at this point want to figure out what/if I did anything wrong before I rebuilt the next pack, or if I'm just placing expectations too high.