Before you spot-weld your next sections, prepare the nickel pieces with solder blobs beforehand.
No need to heat up the batteries unnecessarily this way 
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16awg wire so barely needed any heat to get small blobs down (lots of flux which was cleaned after)
cells barely get warm
If the cell gets warm the damage is already done. You will not be able to tell the hot spot where the heat would transfer into the cell.
Just try to think a couple steps ahead.
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So I recently discovered a trend with some pack builders where they are placing a .1mm layer of copper beneath the nickel strip and basically blasting through the copper layer, sandwiching it between the nickel and the battery terminals, resulting in a higher overall conductivity rating for the connection.
What do you all think of this?
Check it out:
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Looks like you have already got some good feedback from @Common_good, @Simeon, and @luastoned, but I want to double down on what they have said.
TLDR: You have made several mistakes here, and trying to fix them now is going to make things worse.
First off: I dont understand what you are doing with the two pieces of 10mm nickel side by side. The one that you did not solder to is not carrying any current carrying hardly any current and therefore is not really contributing to the current handling of the pack.
Since that inner nickel strip isnt really helping, then most of the current will be flowing through the outer 10mm strip which only has 3 welds per cell (well below the recommended 6 welds per cell).
A better choice would have been to weld the first strip down the center of the cells, and the second strip stacked on top of that one.
The BEST choice would be to use more of the 30mm wide nickel that you used on the rest of the cells.
Second: your solder placement.
The whole point of spot welding a pack together is to transfer as little heat as possible to the cells. Heat makes your cells degrade, leading to imbalanced p-groups in your battery. Enough heat can lead to the cell venting/going into thermal runaway.
Have you noticed how pretty much every batter builder in this thread solders their series connections onto tabs of nickel that hang off the side of the cells, most often with prepped solder pads put there before welding (like @luastoned said)? This is to transfer as little heat as possible to the cells, to keep them from degrading.
You have soldered directly on top of your cells, so all of the heat from that solder joint has gone directly into the cells you were soldering on. There is a good chance you have cooked them, and those cooked cells will drag down the rest of the p-groups they are in. I hope you are using a SmartBMS for this build so you can keep an eye on those p-groups.
A better option is take another piece of that 30mm wide nickel, prepped it with several solder pads before welding it to your cells, and then spot welded it in place. Then you can solder onto those pads with the nickel hanging over open air, transferring far less heat to the cells.
The BEST option would be to prep both pieces of nickel, then actually solder the wires to them, all with the nickel off the battery. Then spot weld the joined nickel pieces to the cells, therefore transferring no heat to the cells. Here’s a pic of what I mean:
Lastly: your wire placement.
@Simeon summed this one up nicely, you should have spaced your wires out better. Right now, all of the current from the long p-group has to flow down to the end of the group, and will be bottlenecked by that thin 10mm nickel strip and small number of spot welds (as discussed in section one).
A better option is to space your wires out evenly across your p-group, so every cell has a equal current path to each wire.
The BEST option is to do one continuous bus bar like the pictures I posted above, so the current can flow continuously from each cell.
Now why did I say that fixing these problems will make things worse? Because as I mentioned above, there’s a decent chance you have already cooked your cells. De-soldering and re-soldering now will only transfer more heat to the cells and cook them more.
If you really want to fix these problems, then the best option I can see is to rip up the nickel that’s on there currently, solder up a bus bar like the one I pictured above (off of the battery so you dont transfer any more heat to the cells), and spot weld that in place.
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hi so a couple things.
first thanks for the advice really useful.
second with the 12mm nickel strips i tried to create a solder bridge between them when soldering the wires (took place after the picture was taken) so i thought that may help.
second i have been told before soldering quickly between the cells shouldnt cause to much of an issue. (they are 16awg so go pretty quick) (and told by a few battery builders here)
third there were 6 welds on each 12mm nickle strip (per cell)
i should have placed the wires better i agree and i prob shouldve used wider nickle.
thanks for the advice though was really helpful and i will take it into account for the next pack
thank you again
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Sure thing, just trying to make sure that everyone has the info they need to make their packs as safe as possible 
Can you send a picture of what you did? In my opinion, that probably just cooked your cells more without much benefit. A better choice would have been to join those two nickel strips with a 3rd nickel strip, and spot welded that on.
I disagree with this. The largest AWG wire I would feel comfortable soldering directly above the cells like that would be a 24AWG balance wire.
Anything larger requires several seconds of consistent heat to get a good solder joint. Your solder joints (while a bit uneven) look nice and shiny, so that tells me that you got them good and hot. That’s a good thing for the strength of the solder joint, but a very bad thing for the health of your cells.
I see that now, my bad. Good job avoiding the center 3mm of the cell 
Sure thing man. I dont mean to sound like dick. You have clearly made a lot of progress on battery building. But batteries are extremely dangerous. They are not really something that you can just “learn as you go,” you know? All of the info I have given you in this post and my last one has been stated and repeated dozens or hundreds of times in this thread and many others.
Learn from other people’s successes and failures, otherwise you are bound to never meet their success and bound to repeat their failures.
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gonna add that now (in the areas to the left of the solder)
seen on this thread quite a few people who have done it and been told by many more that they do it. (even with larger wire)
thanks
of course totally understand this. i have tried to not repeat others mistakes and the stuff above i never realized were issues. will def be corrected for next time
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Be careful you dont spot weld on top of solder. The solder will explode and splatter everywhere.
Some people (most often ebike builders on youtube amd Facebook) feel perfectly comfortable exclusively soldering their battery together, no spot welding at all. It’s all about the level of risk and cell damage you are willing to accept.
Any amount of heat to the cell degrades it to some degree. Limit the heat, and you limit that degradation. Is the amount of heat you transferred to the cells going to make your battery explode? Maybe, probably not, I dont know. Would your battery perform better and last longer if you had not put that heat into them? Yes, definitely. Maybe a tiny amount, maybe a lot, but still.
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It looks good outside of the direct solder for ur pos and neg wires.
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I have no idea how this works lol
How are the nickel strips going across the top of the pack like that
How did you get that much solder in one place
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Those solder joints look really cold and dont have enough solder. That said, just like I am telling Shua in the last few posts, soldering directly above the cells like this is really damaging to your cells.
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Looks like that pack alone was like 500+ welds due to all the nickle tabs XD.
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added some (across 4 cells) 15mm strips (had a couple small pieces lying around.
i think that should be ok now
i agree that it degrades to some degree and the truth is that we here build batteries to a higher level then just about any other place does. (you should see the atrocities in escooters and onewheels)
i agree best not and def wont in the future but i doubt its worth binning this pack over.
if you disagree please tell me
Man fuck my stock escoot pack that shit was made with some cheap ass cell and was just ugh i hated it.
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Had no real choose normaly i try to prevent most of the time but i didnt have a lot of space left and the copper wires wouldnt let me heat it properly it sucks the heat so good… My T12 solder station couldnt keep up.
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I see u had enough space on the side that u couldve spot welded a longer nickle tab to fold onto the side then solder ur main connections on.cause the spacing was big enough for u to slot ur bms right next to the pack after all. It mightve interfered with ur 3dprint mount screws u used but with a good placement it couldve worked no doubt
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That’s because esk8 is a MUCH more punishing environment for a battery than an ebike, an escooter, or a onewheel. We get much more vibration transferred to our packs. We also pull many more amps than just about any production PEV of any kind. That raises the stakes a lot.
Also, the companies who make those atrocities have made the business decision that it’s worth cheaping out on their batteries and accepting the number of failures that will result in. They have their bottom line in mind, and they are confident they can resolve issues when the arise by throwing more money at it.
Are you willing to make the same calculation for your own safety?
If that were my pack, I would not bin it. What I would do is this:
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We do indeed need alot of amps to get the same power output as something like a escoot tho they only need 100 or less amps and can do 40 to 60mph.
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