Anyone ever mod their laptop battery to have more cells in parallel?

Hey forum, just curious; have any of you nodded your laptop battery, by adding some more cells in parallel to the already-installed cells?

The reason I ask this is because the more I look around, the more I see manufactures decreasing battery capacity (Watt-hour), even when there is still lots of room inside of their laptop to fit lipo’s (flat cells, Li-ion are cylindrical, like 18650’s).

Aside from manufactures wanting to save a couple bucks on cell sizes, along with wanting to convince people to spend hundreds more on their $1000+ laptop which have larger batteries, I don’t see any reasoning behind laptop OEM’s doing this, and it’s frustrating.

Anyway, back to my main question, has anyone on this forum actually done it? What did you learn from it? What would you do differently? Was it worth it the hassle? I know people have done it in the past (seen laptops on EBay with mods like this).

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I tried this once. But I removed the current cells and got smaller ones that in total added up to 24% more capacity. It blew up eventually but it lasted longer for sure.

I’m just bad with that sorta thing lol.

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Don’t do this, charging circuits in laptops are designed for the batteries provided. Doing this, especially with lipo batteries is a huge fire risk. Don’t mess with batteries unless you are a trained professional.


Trained professional is a bit much, though you are absolutely correct without the proper safeties in place the risk of damage and fire are too great.

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I’ll just leave this here:

TL;DR version: the more cells you add, be it sequentially or in parallel, the higher the chance of overheating and combustion becomes. Cells’ builtin safety measures fail to protect the battery altogether, so you need to monitor every cell externally.

(which is why I’m very cautious about Tesla and other electric vehicles: they use the same 18650 cells as in notebooks, but in extremely large quantities, and I doubt that manufacturers are monitoring each and every cell)

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What I was planning on doing is:

  • checking what the max charging voltage of each individual cell is (ex. if they are 4.35V, then find LIPO’s that support up to 4.35V), and adding similar speced cells (in terms of voltage, don’t care about matching mah capacity)
  • Adding the cells only in parallel, since I would have no smart way to control the cells in series
  • Each individual cell that I do buy would have a protection circuit built in, to prove over charge/discharge protection (technically, the original BMS on the pack would handle this, but it doesn’t hurt to be extra safe).

Wish I found that document sooner. I just went straight to the conclusion, and it sounded very interesting, however, because of it being 40 pages, I can’t dedicate enough time in a single sitting to check it out. However, thanks for linking this! :smiley:

I’ve messed around with LIPO’s, LI-IONS, and Li-Phoshate cells in the past (taken them apart, shorted them up, blew them up, burned them, charged them, discharged them), so I feel as though I understand them pretty well, in comparison to most people (they really aren’t as scary as less-educated people make them out to be), however, the reason I asked this question is because I am curious as to how others tackled this project in the past, and how to do it successfully.

Care to explain in detail what you did? I personally don’t plan to remove the current lipo cells inside, only add more cells in parallel to the existing ones, but I am curious what you did, and what went wrong.

When the original battery of my netbook died, I did buy a huge battery that fitted it.

It basically went from a 2200mAh 3-cell to a 14400mAh 12-cell. When this battery was new I used to get close to 16 hours on a single charge, and that’s actual use as opposed to the original’s 3 hours in lab conditions. 5 years later I’m still getting over 12 hours.
As an added bonus, the extra height allows me to use it in bed too without having to worry about covering the air intake at the bottom.

I haven’t noticed any issues with charging, it just takes a lot longer than it did before. The original battery was full in little under 2 hours, this one can take 12 hours if it was completely empty.

Would I buy it again or do a similar hack myself? Probably not. I wasn’t aware of the risks involved back then. Now I only plug it in when I’m awake and nearby. So far it hasn’t had any issues though.


Just stop. Mixing different cells is sending alarm bells for fire. This is why I said only professionals. There are things you wouldn’t even think of considering that would cause risk. I have studied electrical engineering to a degree level and what it told me is don’t fuck with what you don’t know.

Buy an external battery bank if you need more power

What exactly are you thinking is going to cause issues? You keep saying not to do this, but you aren’t explaining why things can go badly.

Varied internal resistance of different cells, even with the same label but from a different batch can differ greatly. If put in parallel, there will be a disparity in current between cells. The average charge will appear lower than the real charge of some of the cells. The charging circuit will only see the voltage available for the whole circuit and since it will be lower than it should be, will continue charging the batteries overcharging some of the cells and boom, fire hazard.

This is almost as bad as the guy who wanted to Daisy chain UPS’s

Chill. OP has already made a step in the right direction, choosing cells with the same level of degradation. He’s asking questions which means he’s not reckless. There may be problems, but theoretically they’re solvable. He’ll probably have to monitor every cell’s voltage, charging current, internal resistance and temperature and be able to disconnect any specific cell at any time.

If you’ll have the time, just google “nasa lithium” or something similar. I’m sure they have published even more research and guidelines since this one (especially after their simian robot spontaneously combusted right in the lab while charging up).

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While the battery worked it also caught fire. I don’t think I’m quite the authority for this one, though, bbishoppcm on yt might have something for you.

I haven’t heard about any DIY powerwalls catching fire yet because of all the varying resistance cells…

Correct, cells with a lower capacity will be discharged slower, to match the voltage of the other cells that are in parallel.

A BMS is suppose to actually control this, and not allow this to happen… which I expect Dell to have implemented inside of my current laptop battery, like basically every OEM does for their laptop batteries.

That I can agree is a bad idea. So much electrical noise because of modified sign waves…

I have taken a drill battery ( 18V ) and temporarily used it with a cut off power cord (just spliced cord from wall adapter) to power a laptop… wish i had a better way to connect the cord to the drill batteries.

The main issue you’ll run into is balancing the charge across each cell. When you charge 18650s or flat packs in series or parallel they should really be charged individually, which is why you see so many pins on 6cell and 9cell connectors. I tried to rebuild a laptop battery once out of recycled cells, it ended up working but didnt fit back into the battery case.

Also you should match capacities with your current cells, which means you have to disassemble your current battery and test those cells for actual capacity, or you have replace your current cells to match. You cant just match nominal voltage. What happens is when you mismatch capacities you get varying voltages from cell to cell. As they discharge, cells with higher voltage are doing more ‘work’ and heating up more than the others. This can lead to failure sooner than you think depending on the discharge rate. I’m not sure what modern laptop amp draw looks like. So long as the cells are all within a few hundred mAh of eachother I dont see a problem. At least in the short term.

The 18650s in most laptop batteries are spot welded to tabs to make them space efficient, its hard to produce the same slim design with just solder. Plus you have to include a protection circuit for thermal runaway as well as current protection. In my mind flat pack is the way to go since all thats built in but finding a configuration that suits your setup would be difficult.