Replace individual battery cells to renew/increase capacity

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On the laptop battery suggestion I found that new laptop batteries packaged for dell laptops cost less $/kwh ($.17/wh) than the china pouch cells i'm currently testing ($.27/wh). the question is do these inexpensive laptop batteries really have the 54wh or whatever capacity that is printed on the battery case. and how much time is required to libertate 4000 cells from plastic cases with 8-cells each in them. also I found there are people who take apart laptop batteries and sell the individual cells in places like Lithuania, and these are as little as $.10/wh, but the capacities range from 1ah to 1.5ah, so they would be mixed and I would need a lot of them. a different angle on it would be the 26650 format battery which also has a strong market pretense and higher per cell ah rating, but these round cells may not pack into the leaf battery case at 40kwh volume due to the interstitial space between the cells. maybe that's a big deal maybe it is not. if most of the battery was in the case and then more of it outside the case, in a second place, then the BMS wires would need to run out of the battery case to balance charge the remainder of the pack, not elegant. thoughts?

if I had a leaf battery shell I could do fitment trials, anyone know where I can get one inexpensively? I'm near Toledo ohio.

I also made the discovery that the 2s3p probably is not going to work with the cells I bought, the reason is that the Nissan metal case modules nest inside each other a little and the difference in the overall height and the nested height is going to prevent 6 cells being stacked. The 37ah cells are not near as wide or long as they could be, but they are more than 1/2 the format of the Nissan cell, so two are larger than the Nissan cell when laid next each other on one layer. they do make 50ah cells with the right size which would net a 100ah capacity in a 4 thick arrangement, but I cannot find 60ah pouches that will work, ie both tabs on one side and <9mm thick. as it stand just using the 37ah cells in the stock 2p2s arrangement will net 26kwh with TMS, more than stock and able to DCQC better than stock, but not the 150 mile range I was targeting.

So far the liquid cooling trails showed me that when the 2s/1p pouch cell pack is insulated on the top and bottom, but not the sides, I can charge/discharge without any cooling at the 30amp rate and the cells stay below the manufacturer 113F limit. I found that they get hotter on charging than discharging at the same current flow. and the copper plate with cooling blocks glued on the edge and the particular of the cooling system I have (small 110v aquarium pump and 3x120mm CPU cooling radiator) cool the cells so that the peak temperature is 8 degrees less at a 30amp charge (92f vs 100F with 80f air), and also the cell bulk temperature returns to albeit temperature more than 90 minutes sooner, that's the big difference there. so the next step is to increase the flow of the coolant and try to hold the water temperature at 5 degrees less than air temp by dropping ice cubes into the water reservoir periodically to simulate the chiller cooling the heat transfer fluid below ambient temp just a little. any other suggestions? maybe I could get a second 30 amp charger and power supply and run them in parallel and get the actual charging rate of a DCQC.
Only testing can answer your question! For me its look too difficult to do. I mean the result is not worth it. However, if you like doing it, I'd be happy to see how it ends.

18650's looks good for your purposes, i think.
Looking more into it. If i go with two layers of 26650 cells formed into a rectangle 11 cells side to side and 3 cells end to end might be a pretty good solution. maybe leave out 4 cells per layer to let the 4 retainer bolts pass though . it would take 2784 cells to pull this off. at ebay prices of $2.7/cell (for 6800mah cells that have an actual capacity of 3500mah) it would be $7.5k in cells. the Nissan module is 40mm thick, 300mm long and 225mm wide. if the two layers of cells are staggered 1/2 of cell over then the thickness per payer will be less than the 26mm*2=56mm, closer to 35mm leaving some room for copper sheets that could still be Incorporated in a corrugated shape for active liquid cooling in the same way as the pouch cells.

The best part is that even with a reasonable 3500mah/cell the pack capacity will be 101ah with 29 cells in parallel, and the total energy would be 36.5kwh. Then if ~$.5 more per cell is spent to get real 5000mah ones it still should fit in the stock case and provide 52.2kwh.

I have a spot welder and nickel strip so the construction of the module should not be a limiting factor.
Here is my data for the cooling tests i did. overall the cooling plate between the cells is very effective, and chilling the liquid below ambient temp is worthwhile. with only ambient air to cool the liquid which was a 9 GPH flow rate, it lowered the lithium pouch cells peak temperature 8.4F from 25.6F temperature increase with no cooling to 17.2F with cooling, and then lowering the liquid cooling temperature ~8 degrees below ambeint with ice cubes dropped periodically into the reservoir lowered the cell temperature again to a maximum temp rise of 12 degrees F. The follow-on effect was that after charging was complete the cooling effect from the plate cooling system quickly dropped the cells back down to ambient temperature, or very close.

on the discharge side of things the heating effect was less, with the non-cooled cells reaching 18 degrees temp rise at a 30amp rate and with liquid cooling it was about 11 degrees, the same amount of benefit as the charging scenario.
looking into the 18650 batteries further it looks like there are some promising options, but I also really have a concern about the laptop battery approach. namely laptop batteries are considered by many to only have 400 cycles of life, and premium laptop batteries 800 cycles. I would not want to go through a bunch of effort if the battery is at a large degradation amount after only 2 years or so.

on the upside, the cost is amazing. I found that buying new high drain laptop batteries can get me a guaranteed 2600mah cell for $1/each delivered ( Since the 18mm diameter is slightly less wide than the 26650 it would be possible to have 16 columns of batteries and since they do not need to be nested, the bolts can fit between cells since they are stacked strait up. cramming a total of 4608 cells in would give a pack capacity, new at least, of 44.3KWH for less than $5000 in cells.

I also looked at the fitment into the Nissan leaf module. using 200 amps as the momentary peak current draw I find that 1awg wire would probably be OK. 1 AWG has cross sectional area of 42.5mm, maybe someone can measure the bus bar in a pack and report how thick and wide the conductors are. anyway, using 1mm/40mm conductor in the module will be very low resistance and I came up with a nested "L" layout with only one place where two conductors need to be between cells. have a look:
Nice project!

ripple4 said:
looking into the 18650 batteries further it looks like there are some promising options, but I also really have a concern about the laptop battery approach. namely laptop batteries are considered by many to only have 400 cycles of life, and premium laptop batteries 800 cycles. I would not want to go through a bunch of effort if the battery is at a large degradation amount after only 2 years or so.

on the upside, the cost is amazing. I found that buying new high drain laptop batteries can get me a guaranteed 2600mah cell for $1/each delivered

I have tested a lot of 18650 cells, currently building an EV with them.

These new 1$ 2600mAh cells might be tempting, but remember that these will also degrade to about 2000mAh after 2 years. By starting with cells that are specced at 3000mAh+, but has degraded to 2200mAh, these cells will not change that much in the future since the worst degradation has already happened. This ofcourse depends on the cell brand, etc, so no real ultimate solution.

Also laptop cells are charged to 4.2V and discharged all the way down to 3.0V. So by using them with a leaf BMS, they would only charge to 4.1V and discharge to 3.5V under normal use (3.3V occasional turtle), which would increase the amount of cycles they can do! So an EV application is easier on them compared to a laptop. (Laptops also stay at 100% SOC for most of the time , which is not good for the cells)

Do you need any measurements etc? As said, I have a leaf cell and heaps of 18650 cells.
Cool sounding project if you make a post about it please PM me, or link it here.

I was researching the excellent suggestion about laptop batteries having short life because of their high utilization strategy in mobile electronics, and battery university website backs this up. ( It in fact show how much longer one could expect in various charging scenarios. right out of the gate, they say for every .1v that the cell is not charged under 4.2v it doubles the life, and not storing at high charge levels increase life a further 20%, those are freebies with no behavior change. going further, shallow cycling really increases life proportionally to depth of discharge, so where a 100-25 charging pattern might expect X cycles full life, 85-25 would have 2x cycles, and 75-45 would have 5x cycles. expanding capacity to 44kwh will allow very shallow discharges on a daily basis while allowing for 100%-25% 150+mile long trips occasionally. the temperature aspect of it also supports some kind of TMS as heat reduces life.

The only technical issues i can anticipate is that the 80kw acceleration will draw ~220amps from the pack, with 48 parallel cells each one will need to have a peak draw rate of 4.6 amps for at least a few seconds, that might be above what a laptop cell can provide, not that high drain and high capacity 18650 cells don't exist, but they are not $1/each.

Thinking on assembly, i think that using nickel strap material will be needed to connect the cells to the modules internal buss bar, 1mm thick copper might not spot weld easily to the cells, and will prevent any kind of service, whereas if we get 12.7x.25mm nickel strapping and make connections to the bus bar that way i can spot weld everything much more easily and then fold the bars flat to the pack afterwards, the only thing left after that is creating the copper to copper buss bar connections. I want the design to be manufacturerable in anyones basement or garage. maybe the cross bars could be nut and bolted in to maintain serviceability, also i would make the connections on the top of the pack now, to maintain access for cooling hardware on the back of the cells.

it would be great if someone could help test the modules in a car, while i am working to someday make a pack for my car, I commute a long way each day and my 2012 cannot be down. I might consider buying a 2011 leaf with a nearly dead pack, or crash damage etc as my test mule.
Here is the latest plan for the inexpensive 2012 Nissan leaf cell with more capacity. I am talking about a 35-40kwh usable capacity pack in a 2011-2012-2013 Nissan leaf with active TMS. there seems to be a large supply of the new 2600mah 18650 cells from ebay laptop battery sellers and with cooling and shallow cycling I can see these will last many years and thousands of cycles, if all else fails the extra pack capacity will allow for more degradation and still be useful.

I determined from watching several videos and reading about how tesla and BMW are cooling their cells that tab cooling the cells, as opposed to body cooling the cells will have a more effective result of increasing cell life. both tab and body cooling are a possibility. see video ( so I think installing silicone heat transfer pad between the ends of the cells and the bus bars will allow the bus bars to be dual use electrical and heat conductors. to connect the cells to the bus bars I plan to use .25mmx12mm pure nickel strapping to connect up to two cells in parallel per strap to the buss bar, which will have a current density of less than 4amps/mm^2 with is the good zone ( then I found a 200mm long water cooling block and with the same silicone heat transfer pad I would connect the ends of each buss bar to the cooling block. the silicone cooling sheet has a dielectric strength of 4kv, so it will allow thermal transfer without electrical transfer. Or I could use mica sheet and thru-bolt the copper buss bar and water block for better performance since both surfaces are flat and stiff.

totaling up the cost of cells, the 1mm copper sheets, water cooling block, silicone pads and nickel strapping I'm at about $144/module. can anyone see a way to cut cost out while still keeping manufacturability and functionality?

module cross section:

overall pack visualization:
The laptop batteries that I bought did not work out. I had 11x 9cell batteries shipped in from that ebay link and once I opened the packs and tested individual cells, the truth was revealed. In order to get the 7800mah energy advertised, each needed to be 2600mah, but when tested they were barely 1100mah. they weighed 40 grams each which is consistent with that energy. also one of the batteries did not have wires to balance the cells, just a +/- from the ends of the pack, I thought that was a fire risk.

I guess the two takeaways is don't buy cheap batteries for your laptop, and don't expect the rated capacity at $1/cell. The 1100mah cells would not even have the engery level of the stock 24kwh pack, so that's a non-starter. anyone have a place to get 18650 cells in the 1800mah-2800mah real capacity cells at a 5000pc quantity for a low price? the next step for me would be looking at 26650cells at the 5000mah level and going that route.

Also I notice on these cells that the energy going in from the charger is noticeably larger than the energy released on discharge compared to the 37ah pouch cells. it was just an casual observation, but I'll look into it more. this is called the round trip efficiency I believe. I still have some of the batteries because the ebay sellers did not want the cells returned once I reach out and told them the issue.
A note on the laptop-sourced 18650 batteries, looks like electronics and power electronics application are going to differ quite a bit, the distinction is called 'high drain' i think. anyway with the laptop 18650 cells the round trip charging discharging efficiency at 1C was 93%, and the round trip efficiency at 2C was 44%. with 48 parallel cells the current draw per cell on these exact batteries would be .7C at a 20 kw draw, so they would technically work for commuting, but many rapid accelerations would waste alot of power as each cell would be at 3C peak draw at 80kw and i don't think that they can provide that, the voltage sags too much, so high drain is really going to be a requirement.
Update: After trying 5+ different kinds of 18650 lithium batteries, from high spec LG HG2 to no-name generics I’m pretty certain that 18650 is not the way to go. The weight to energy to cost ratio is not where it needs to be, if I could find 3000mah 5amp drain cells for $1.50 each, it would be one thing, I cannot. As it stands the best 18650 I tested had 1600mah between 4.13 and 3.3 volts at a 1.5amp discharge rate, and weight 42 grams and costs $1.75. Fitting out the pack like I showed in a previous post with 4700 cells total ends up at a specific energy of 7grams/watt hour and the cells would cost $8100 for pack energy of 28kwh.

Now the update is the EBL 26650 cells I got my hands on. these guys provide 4.8AH between 4.13 and 3.3 volts are rated at 1200 cycles, which is 3x longer in shallow cycles, so its there. I am hoping that I can get these for $3/each (currently $4.35/each from ebay), and in the high density arrangement I came up with, which I think is really cool, I can get those numbers to move in the right direction. The specific energy would be 5.0gram/watt hour, and a pack energy of 47.5kwh and a cost of $7800 in cells. There is a lower density layout that is 37.5kwh and $6K.
My next steps are to find a high volume-low cost supply for these batteries and again, make one module and test the cooling approach I talked about before. I didn’t have a chance to test it on the 18650 because I didn’t want to waste the copper bus bar materials since the cells could not have worked.

I did find a new tool to help investigate cells, I found that if I X-ray them I can see how many wraps they have in the cell, how big the center pin and from that the square area of the electrodes. The 18650 that performed the best had a center pin diameter of 6.5mm, and 19 wraps of the electrodes, this means each wrap is .29mm thick and it has 13,000mm^2 of area. Then 26650 has a center pin diameter of 3mm and 31 wraps for an electrode area of 26,250mm^2, twice the 18650! And the energy works out to 5mm^2/milliamp hour for the 26650, and 8.3mm^2/milliamp hour for the 18650. The EBL 26650 also has a thicker layers at .37mm, so that might indicate durability or other robustness.

Also I really could use an empty battery shell to do fitment work on, if anyone knows of one in the SE Michigan area, please PM me. Lots of people sell the leaf modules, but the cases must be scrapped.
Hi - do you happen to know where Nissan is as to whether they will allow their own shops to replace individual cells? Maybe this is common knowledge, but I have just been wondering about it and ran across this DIY type of thread.
jlsoaz said:
Hi - do you happen to know where Nissan is as to whether they will allow their own shops to replace individual cells? Maybe this is common knowledge, but I have just been wondering about it and ran across this DIY type of thread.

Yes, LEAF-certified Nissan dealers can replace individual modules if they become defective (not just capacity loss). There are a few reports in other threads on this site.
GerryAZ said:
jlsoaz said:
Hi - do you happen to know where Nissan is as to whether they will allow their own shops to replace individual cells? Maybe this is common knowledge, but I have just been wondering about it and ran across this DIY type of thread.

Yes, LEAF-certified Nissan dealers can replace individual modules if they become defective (not just capacity loss). There are a few reports in other threads on this site.

Ok, thanks, good to know.
Feel free to use this invention/design for any non-commercial application. For commercial applications contact me and we can work something out. I completed a micro pack assembly to test out my process and also test how well the silicone heat transfer pad will cool the cells in the micropack before building a full size leaf module. The U shaped micro pack will show the ½ thickness buss bar that will be in the full size module between – and +, and the remote cooling blocks will allow the buss bars to also act as the cooling heat conductors.

The hard part about assembly is the devilish details in the process of attaching all the parts, I wanted to make it so that with modest cash the process could be reproduced, so a multi-hundred dollar spot welder will be needed, so long as it can provide ~1200amps to a parallel electrode weld handle. I made a few handles before settling on my own design. The electrode have to be independently supported by springs to get good welds, once the power hits the metal turns to jelly, and if the electrode comes off the surface it arcs and sprays metal everywhere, its nasty.

The file can be downloaded here:

It uses 2x ¼” diameter 4” long RWMA class 11 (75% tungsten 25% copper) electrodes threaded about ¾”up each end with ¼-20 threads, the points were formed on a drill press with a lathe cutter in the vise and the threaded the same way, with the die in the vise. That way it threads strait, tungsten copper is hard. Also this way the points and threads can be easily redressed as they wear out. The weld process is direct energy AC with a phase-fired SCR as the control mechanism, also known as a spot welder. The spot welder I used was a current feedback controlled, 480v/30amp input, but only 5.3v output, but with up to ~2500amps though. The .2mm pure nickel strap takes more power than the thinner, plated steel straps. There are several 3kva/kw spot welders on eBay (SUNKKO 709 or similar) that might have enough power for .2mm Ni, or maybe two layers of .1mm strap could be used. The straps need to conduct 17 amps peak when connecting two cells. And that puts the current density at 6.5amp/mm which is the maximum, 4.5amp/mm is the recommendation for best performance. .1mmx12mm should be enough for single cell connections. hmm..maybe I should only do single cell connections since the staggered cells are not suited for doubled up cells anyway.... To make sure the welds are good, I do a 90 degree pull test, if the welds pull out the strap, and I can see though the hole, it’s a good weld. If the strap peels off in the middle of the weld, it’s weak. The negative side of the battery is thinner than the positive side and so it needs less power, I used a longer 10 a/c cycle, cooler 1000 amp weld for the negative side so the electrode points did not press into the can. Then on the thicker positive side I turned the power up to 1250 amps, but cut the time down to 5 A/C cycles and that was also used for welding two layers of .2mm strap. I used 1 a/c cycle for upslope to cut down on sparking, you tube videos of welding batteries always have spark flying everywhere, that does not make for good welds.

Connecting the strap to the 2mm thick copper buss bar was not as easy as I had thought it would be, it won’t spot weld on. I think I will try blind copper pop rivets for the module assembly, which is cheap and easy for the home hobbyist. However, for the micro pack I laser welded it. I know this is not a practical solution, since multi-kw lasers are expensive, but for the curious, it worked really well and here are the weld details.

My next steps will be to test the micro pack with various charge and discharge currents that represent the important conditions the module will see, just at 2/27ths of the current. Then I’ll wrap it in insulation and measure the heating effect with no cooling, and then with cooling, like I did with the pouch cells, and document what I find.

Here is the assembly steps of the micro pack and how the silicon heat transfer pad is cut, installed, and folded into the module. The picture I posted awhile ago shows this from an end view but in real life the details are apparent. The silicon pad is sticky like chewing gum so it conforms to the surfaces for good heat transfer, I hope.
I hope if someone sees/follows this thread here, they feel free to speak up and make a suggestion or a comment, getting feedback is the point here.

Here is an update on the cooling performance of the micro 2s2p 26650 pack. I found I have to drain the pack prior to starting the charge at the same rate, so both lines here had a 1.2amp discharge rate (7500w simulated motor power, like a slow drive in a parking lot) to 3.3v/cell and the DCFC started right after. The cooling really makes a difference in a way I would not have expected, the pack is able to stay in constant current mode for a longer amount of time with cooling, and so then finishes faster, 15 minutes faster at the simulated 50kw DCFC current rate. The innovation here is that the pack is remotely tab cooled. Or in other words, the liquid used for cooling is only on one side of the module and the heat is drawn out in the same buss bars that conduct the high currents. And where the cooling effect interfaces the cells is on their tabs. Like I linked to in a previous post this arrangement is supposed to cool the cells from the inside out, and lead to longer life.

I’ll get some back up runs to confirm this. Also do a run with ice in the reservoir for simulated refrigerated cooling . This data is only using ambient air passing through a CPU water cooling radiator, no chiller yet.

Also I did some work developing the nickel strap to buss bar rivet idea. The rivets did not form how I wanted out of the box. It had a long tail end and I can rotate the strap on the rivet, not good. I figure I can just crush that in a press/vise with smooth jaws and can get a nice crowned back, so its strong and it does not rotate then . I’m waiting on .15mmx10mm nickel so when I get it I’ll make the 18 rivet / buss bar sample and post how that looks.
I've also been considering a complete pack replacement with the newer 5000mah 21700 cells. It would take about 2,000 for a 36kw pack. I've seen them for $5 per cell in quantities of 1,000 or more. Definitely not cheap even with an extra 50% of range.

They would be packed without the plastic sleeves for better cooling in 48 3d printed plastic modules using the stock bus bars and connectors. The cells are much lighter than stock so the pack would weigh about the same.

$10,000+ for a battery pack is too much so in the meantime I'll be checking the pack with Leaf Spy and see if I can refurbish it by replacing the lower capacity cells with good used ones. The cost could be well under a $1000 if not too many cells are bad. Even that is not cheap considering the range might be extended just 15 to 20 miles. But as any Leaf owner knows, that extra range is like gold!

How do you hook up multiple cells to coolant using conductive bus bars?
OK I understand how the coolant lines are insulated by the rubber tubes.

There's another cost effective option to replacing the entire pack with new cells. Sell the old Leaf and buy a 2013 or newer model that has had the pack recently replaced with a lizard pack. The prices aren't that much more. I've seen them for $7,000 to 8,0000. Subtract the sale of you old car and that's just $3,000 to $4,000 to upgrade with very little labor.