You would be amazed how many battery packs are multiple 18650s in a trenchcoat. Even EV battery packs use them. Though it does raise the question - wouldn't an old EV battery be a better solution than stripping apart laptops?
How good is your cell acceptance testing? Do you do X-ray inspection for defects, do ESR vs cycle and potentially destructive testing on a sample of each lot? When a module fails health checks in the field, will you know which customers to proactively contact, and which vendor to reassess?
Yeah lots of batteries are 18650/26650 in a trenchcoat. The trenchcoats run the gamut from "good, fine" to "you will die of smoke inhalation and have a closed casket" in quality and I think that bears mentioning.
I just assumed there was … special stuff in there
Using a custom cell might make sense if you are making a) one megakajillion of a thing or b) you have extreme volume limits which mean you're probably using a pouch cell.
In HW engineering, Not Invented Here syndrome costs you big money. You have to have an actual business case for re-engineering something that already exists plus the capital.
95% with my stuff of the time COTS cylindrical is the answer, which means my shit comes in on budget.
Soldering some connectors onto some random cells and knowing they shouldn't go over 4.2v is one thing, but measuring cell health via internal resistance, programming a controller to do temp shutoff and wiring up temp sensors, keeping cells balanced, is a lot of extra work, but critical if you at all care about not potentially burning down wherever they're stored.
Keeping the cells small and just using a hundred of them in parallel (and a hundred of these parallel packs in series to get up to the hundreds of volts needed), thus using ~10,000 cells, in EV batteries limits the maximum damage from one cell going worst-case, assuming your enclosure can contain it.
That being said, it seems there is a slow movement towards larger cells, from 18650 to 26650 or similar. But each cell on its own is still a dumb can of chemicals ready to go boom if you mistreat it.
Don't, uh, buy those unless you're sure.
Also with bigger packs inter-cell consistency is really important (good cell integrators will test and bin them by ESR even if they're from the same lot, and using a really reliable cell mfg/vendor is critical because you're selling expensive systems with a number of failure points that scales with the number of cells and you want their process development to be super mature.
Was definitely one of the harder parts of our solar install to get comfortable with.
(IIRC, these packs are 16 100ah LiFePO4 cells in a steel case w/ built-in fuse, breaker, and BMS that monitors individual cell health and pack temperature, w/ automatic cut-off if any of that goes out of spec. The weakness is primarily the MOSFETs on the BMS potentially failing shorted. Fortunately, they've added some sort of additional fire suppression beyond just "steel case" in recent-ish versions of these packs)
Here's a video inside a recycling plant: https://www.youtube.com/watch?v=s2xrarUWVRQ
Also laptop batteries used to be many (usually three or six) 18650s in a plastic trenchcoat.
You could literally rebuild your battery when it died, and pick the cells you liked the most. In theory you could pick higher-quality cells than those you find in the batteries sold on ebay from chinese stores. In theory.
$50 of 18650s in a $500 trenchcoat with DRM protection. So wasteful.
We are well past the point where we should have standardized batteries. We have bunch of standardized wall outlets that accommodate an array of "non-zero chance of literally killing your users" end products. No reason for battery packs to not be standardized (other than vendor lock in).
You're also wrong about standardization - standarization at the cell form factor level is correct. Different applications have different capacity vs power density requirements, temperature range requirements, cost, lifecycle... a pouch cell that goes in a drone looks a lot like one that goes in a cell phone but they're optimized for completely different workloads.
Also we already have standardized interfaces for external batteries with most power banks using USB-C, so in a way your wish has already come true.
https://www.protoolreviews.com/doge-mandates-power-tool-manu...
Probably the only thing I can agree with doge on.
Linus from Linus Tech Tips made a few episodes on building a battery out of individual 18650 cells, and one of the thing he stressed (as in, underlined) a lot on is that spot-welding cells is extremely dangerous and there aren't easy ways to put out a lithium fire.
Water is not only not going to help you, it's going to make things worse.
You __have__ to have a bucket of sand with you and if anything goes even slightly wrong you just toss everything in the bucket of sand and bring the whole bucket outside.
Yeah burying a thing in sand is legit. Depending on the size of the thing that's on fire, water might be fine. Standard protocol for electronics that catch fire on a plane is to apply water to cool the device and extinguish materials around it, and then to put it in a special fireproof bag with a bunch of water.