The battery builders club


High Voltage Cutoff


Got it, THX. I have some trouble shooting to do…or my BMS might be taking a dump I was only at 47V also I’ve noticed that my battery is out of balance (more than normal) while charging. Normally it would stay within .02- .04 but now it’s like .08 .09 while charging. The charger plug gets warm while charging as well. I don’t remember the plug ever getting warm. Anyways thx again.

Anyone in the United States good at building a flexible flat pack? DM me I’m looking for someone to build me one.

Here is a list of a few trusted builders in the US

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Those guys don’t look like they make packs anymore. F it I’ll just get a mboard battery.

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? Most of those people make packs. @JoeyZ5 @Skyart @TheRef all can build you one




So I’m preparing to do my first ever battery build, and I figured a good way for me to test my knowledge would be for me to write out what I think to be the correct procedure for doing it and then maybe someone here with experience could read it and tell me if there are any gaps. The pack is 12s8p p42a. I’ve omitted some of the finer points here since I’m lazy.

Alright, here goes:

  1. Dial in spot welder

  2. I have a maletrics spot welder and one 3ah 75c “turnigy graphene” lipo. I’m assuming this power source won’t be enough, so I’ll likely use a car battery.

  3. Proper spot welds should have some color to them but should not look super melty. Welds can be tested by tearing the welds apart. The nickel should fail before the weld leaving material on the cell, and in a messy way (bending and tearing of the nickel should occur, the break should not be clean)

  4. 3 pairs of welds per side per cell is good.

  5. Avoid center of cathode of cells

  6. Test cells

  7. Measure cell voltage and capacity. All cells should be balanced to the same voltage and cells of differing capacity should be distributed so that p groups generally have very similar capacities.

    1. I got my cells from 18650 battery store. The cells are all within <.01v out of the box. I’m assuming I can omit the capacity testing step since it seems likely the cells are very close in capacity?
  8. Mechanical cell connection

  9. Hot glue cells together in sets of 4 in a row and apply fish paper rings

  10. Pair up sets of 4 into sets of 8, glue together wrap in fish paper

  11. Question: how are the groups of 4 combined into sets of 8? Where do you apply glue?

  12. Extra tape cad be added at this time for structural integrity (strapping tape)

  13. Nickel + series connections

  14. Question: I’m using .2mm nickel from mboards, is there any concern about this being a bottleneck for the pack?

  15. Scratch up tabs so nickel can be tinned

  16. Clean nickel (i plan to use 99% isopropyl alcohol)

  17. Add pools of solder to roughed up tabs so that series connections can be made quickly later

  18. Due to the large amount of contact with the wire desired, it may be best to solder the main xt90’s leads to the nickel for the first and last p group before they are soldered.

  19. Question : would it be reasonable to leave an extra one of these leads in the pack at the other end for a potential future upgrade to 4wd? In the meantime i’d probably use a loop key like jumper so it can be ignored.

  20. Weld nickel to cells

  21. Add little u shaped 12 awg wire pieces for series connections, 2 per connection is enough. They should not touch each other ideally.

  22. Thin closed cell foam can be added between the nickel sides of adjacent p groups to make the pack more flex tolerant.

  23. BMS

  24. Wire as per given diagram, don’t let any balance leads cross, if they have to make a fish paper bridge. As usual for electrical stuff be sure to implement strain relief and make sure nothing could rub/abrade or slice wire insulation.

  25. Finish

  26. Probe balance leads to make sure correct voltages are seen

  27. Once bms is installed, check the smart bms app

  28. Wrap pack in heat shrink or more tape, add foam padding before installation in the enclosure.

  29. Safety

  30. Eye protection while soldering and welding is good

  31. Fume extractors/methods of not breathing soldering fumes are good

  32. Plan for what to do in case of cell combustion (sand bucket or place to throw cell/pack) is good

Any and all suggestions are welcome and appreciated. Thanks for reading!

E: sorry abt the formatting, I’m not really sure how to fix it


What causes this, checked the charger and wiring. Everything checks out. Fused charge port…4A charger 50V. A few weeks back I lost the charge port cover so I used some tape to cover it. I replaced the cover. Is it possible some tape residue got inside and caused the plug to heat up?

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very likely

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Sigh this is a super long post but pretty much everything you said sounds good

Check out my vid here that is basically exactly what you’re doing and let me know if it is useful

I’ll try and read it again later if I have time


Am I a joke to you!?


That’s a good list and you’ve covered many key points. One that you missed was checking the voltages for each p group in progression once you’ve completed all the series connections.

Additionally, I’d skip checking capacity for cells. They will be very consistent from any established cell manufacturer and checking the capacity for 50 or a 100 cells will take you weeks. This will seriously extend the amount of time needed to build your pack and will lead to fatigue and some frustration in my opinion

Use new cells from an established vendor and you don’t really have to worry about this bit. Opinions may differ but that my $0.02.


Well fack I missed this verbiage. Sorry for the redundancy lol.

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I figured you’re too big of a deal to work on a single lowly battery pack. <3


Anyone k ow the best place to source cells in Canada? 18650canada is a scam and last time I ordered from the states the shipping fees from DHL were almost half the cost of the package.

Where did u order from? Bulk battery doesn’t use DHL… at least to ON

I’ve yet to find a legit vendor in our country.

Updated the charge rates table.

Added about twenty new entries and the Molicel “standard” charge rates too. These are all rates from the datasheets with a “MaxLife” rate set by me that’s about 1/2 the standard rate. Try this rate if long cell life is your priority.

If a cell is not in the table, I do not know its charging ratings.


First time programming an LLT bms. Can someone have a quick peak at my settings?

Hi builders - question for ya…
One of my boards has a 12s3p (p42a) in it and I need it to be a 12s4p.

The 12s3p is a couple years old but still holds 10Ah (at least according to my satiator charger it takes 10Ah to charge to full) so it’s still in decent shape.

No one wants a two-year-old battery tho so it wouldn’t have much value.

So the question then: toss it and buy a 12s4p for $600 or have an extra p-group of p42as added to the existing 12s3p (is that even possible / a dumb idea)?