Quick question: Are the welds on the two batteries on the left good to use? Looks like it burned through the nickel strip. For comparison, all the other welds look like the battery on the right
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I would redo the 2 on the left, also try to wear gloves and keep the nickel clean, I can see fingerprints on it and believe it or not it will have an impact, also make sure you keep the welding tip clean and shiny
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The fingerprint is probably from me inspecting them. I am going to clean the strips with alcohol before connecting them in series. Some of the batteries were shipped in bubble wrap that had some sort of light adhesive on it, and it left some residue. Not a big deal since it should come off easily
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Don’t hold cells by the terminals with bare fingers 
this was my work.
sorry about the burns there, but the additional welds should be good. i did another weld to make up for the burned one.
if memory serves right this happened at the beginning then dialed in the welder settings.
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and this is strictly anecdotal, but i redid a 12s4p pack that was initially soldered together.
when it was welded together again the nickel welds kept exploding due to remaining solder on the cell caps. needless to say the thing is a mess.
but i’ve been using it now for nearly a year with hundreds of miles logged. i check drift about every 4 charges and there’s been virtually none.
not sure what the point is here, just trying to put your mind at ease.
of course, if you’re still feeling uncertain we can work something out.
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My impression was that it was your weld and you weren’t sure if it’s good or not, but being that it’s @thisguyhere and he did what’s needed, I wouldn’t worry
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No you’re good. Wasn’t trying to call you out
Thanks guys! Just wanted to make sure those two cells weren’t damaged. Overall the cells look great, so I won’t worry about it
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Looks like the nickel strip is folded over and gap cause the burn through
What kind of spot welder are you using @jmasta ?
@scepterr do you think it was turned to high resulting in the burn marks?
I just soldered the jst connector to the foot peddle for my arduino spot welder and am trying to pick up on as much subtlety as possible. Dont want to fuck up some batteries.
Also, is it possible to practice on some dead AAs?
It was @thisguyhere that welded it, Couldve been warming up, air gap, probes needed a polish, it can really be caused by myriad of factors.
I actually don’t use the foot pedal on the Arduino, the autopulse feature is awesome
You could practice on some AA though I don’t know what material they use for the terminals…if you have any dead laptop batteries, now would be the perfect time to tear them apart for practice 18650s 
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