Looking for tips for rebuilding power tool battery packs.

if someone needs a copper strip, look for shim stock at macmaster or grainger. they have them all, any thickness, any material

Curious, have you seen many 18650 with tabs? I know that tabbed cells are common for Ni-Cd, sub-C, stuff in the RC car world (or maybe I should say “were” common? maybe li-po took over for high discharge stuff). But I haven’t seen (or looked) much at tabbed 18650s.

Are you sure they weren’t plated copper? I thought the same thing when I opened up my first couple packs, but then when I investigated further (cut or scratched the strips) they were all copper underneath.

i cut them, so i’d see if there was a copper under, i actually still have a strip from dyson v10, i’ll post picks when i come home,
also it makes little sense to plate a copper with nickel, the benefit of copper’s lower resistance will be thrown out if you plate it with nickel, your strip will have resistance of nickel, since electricity flows outside the conductor, might as well use cheaper nickel strips.

maybe it was steel, copper plated first then nickel plated, copper plating is excellent base for other plating over it, it sticks good to almost anything and almost anything sticks good to copper, but copper is pretty bad for spot welding due to lower resistance, thus higher resistance nickel is used for plating so it can easily be welded with spot welder. to spot weld copper you need special mini arc welder

s. now that i think of it i still have a cell from ryobi pack with pieces of strip still attached, i’ll post pics of it too

I also thought about replacing cells in some old packs, no OEM batteries available.

For nickel strips nkon proposes a service for spotwelding them at 0.5€ per cell, very good price IMO, with some cells at 3€ the whole thing wont be very costly.

But If you’re not in Europe that’s not helping.

About the potential bricking issue I thought about connecting another group of cell to the BMS during the whole replacement process, so that the BMS never see any cells going to 0V.

Seriously? They’re pretty common, specifically for doing battery packs, etc.




among others.

They ain’t that hard to get. Definitely a plan…

I have built a couple of battery packs before, I used a 240 watt soldering gun to solder on tabs. Lots of heating power for a quick solder joint.
I dont think that heating the actual case or the lithuim in such a quick or small amount can actually hurt the battery.
What purposes the danger with soldering onto the cell is the way the lithium sheets and anode and cathode is connected.
Since the anode (-) is connected to the case of the battery the cathode (+) is probably the more dangerous end for over heating.
What connects the lithium sheets to the anode and cathode is a tin strip that looks to be spot welded to each.
If this tin strip comes lose from either end then the battery is dead, no connection from the lithium sheets to the outside.
If the tin stip comes lose from the cathode (positive end) then its hanging lose on the inside of the battery where it could touch the battery case which is negative and a direct internal short. :open_mouth:
HKJ has a few pictures that might help with understand what I mean. This is just my observation of how a lithium battery is designed.

you’d need a battery tab welder at least. You can get pretty decent high drain 18650s for ~$2/ cell, so if you have 4 packs to do you could easily do so for $200 or so, depending on which tab welder you get. Don’t bother trying to solder the cells - not from a damage perspective, but from having to fit the cells back in the case. There’s not much spare space in there!

As for disconnecting the BMS board, that’s a tricky one. I’ve recovered bricked batteries by charging individual banks, but the only time I’ve rebuilt a battery (large 40 cell ebike battery) and disconnected the BMS, it didn’t work ($800 mistake right there). I do have a lawn mower battery I’d like to build using a spare board, but I’ll wire in a “dummy” pack first to make sure the BMS lights up. One way around this when rebuilding packs is to hotwire in a “dummy” pack of the correct voltage, remove the old cells, add new cells and then remove the “dummy” pack. Not done this myself, but the theory is sound (make sure both old pack and “dummy” pack are at the same voltage) and I’ll be doing this the next time my ebike battery needs rebuilding.

Oh, and for high current draw applications, you can use 10mm x 0.1mm pure nickel strips and sandwich a layer of 0.1mm copper sheet between the nickel strip and the cell. The tab welder will weld straight through and make a solid connection between all three.

I had some success with cell replacements in my Makita battery packs. Using a butane soldering iron to solder some copper tabs. Lots of work, and costs for good cells (mid current /capacity as Sam 25R or Sanyo GAs).
Found new clones on Alibaba for cheaper than cells + shipping.

You might also ask among the Li-Ion recycler, Solar, and DIY Power Wall community. They have places like Dirt Cheap Batteries. If you salvage old packs, your price per cell can be well under a dollar. You’ll need a cell tester and conditioner.

I have built battery pack for Makita 18v tools out of old laptop cells.

It is external pack connctet to the tool by a cable. It is less compact but cost me almost nothing and good enough (even better) for my uses.

I solderd the cells with heat and connect the pack to a empty original battery.

You cannot use the original charger so either use hobby charger or protection board and 18v li-ion charger

Sorry, I guess I was thinking about heavy duty tabs that would be appropriate for tool packs / high amperage when I said that. You are definitely right, I have seen cells with tabs like that, but that paper-thin steel tab is good for maybe all of 2A current, so it’s not really going to work for OP’s purpose.


Very interesting, do you have any links to build threads using this technique? Or just more discussion of it in general?

I haven’t heard it before (though I’m far from an expert on pack building) but that sounds pretty promising if it really is that simple.

I have rebuilt NiCd/NiMh packs professionally - we were prohibited from rebuilding lithium (ion or otherwise) packs due by federal regulations.

I can’t say I’d recommend the DIY approach to lithium ion tool batteries. As already mentioned, the electronics tend to brick for all sorts of reasons as a safety feature. Not to mention having to weld tabs somehow. And then there are the legitimate concerns for safety. If we shorted a NiCd cell it would start to get hot and maybe glow or smoke - whoops, cut it out and grab a new cell. With LiIon, it goes worse, faster.

I love DIY ideas and overall the DIY approach. But hope you oversized the pack enough as to meet the drill amperage/power rating. Laptop cells only have around ¼ the discharge rating of good high discharge cells.

EcuBebge, concerning your request, did you properly search for aftermarket battery packs for your drill? There are companies out there manufacturing good battery packs for old drills.

If anyway you want to take the DIY approach, besides spot welding you are better buying cells with tabs or you can also, like me, low temperature solder cells. I use Bi50Pb32Sn18 alloy which melts at 93 - 96° C according to my alloy's packaging sticker:

It can be bought affordably, take a look at eBay merchant zhuykoff's items for sale.

You are also better buying special aggressive flux for steel (here & there, for example). Makes your life A LOT easier.

At last, solder wick is useful for flat cell inter-connections.

The current BMS circuits may be reused. As far as I know they don't use stupid “permanent” self-defusing logic like in laptop packs, so they don't need to be reprogrammed. I don't think this is necessary for such simple BMS circuits but just in case connect cells in sequence from + to − or from − to +.

I saw your other thread about rose’s metal the other day and I was interested in trying this too, thanks for those links.

But aren’t cells terminal nickel plated ? Not sure a flux for steel is necessary, maybe just the fact that it’s more agressive, plumbing flux is generrally very effective because of its aggressiveness, require good cleaning though.

Trust me thefreeman, get flux. Get a single bottle if you just aim to try a little, it's cheap and lasts a good while. First of all, even if a cell looks clean to the eye it may have some layer of debris or rust. Also, once you mess with the cell coating or you need to solder over something with any sort of oxidation layer, you're gonna have a hard time. That flux is liquid and makes the job stupid easy:

Thanks everyone for the responses!

Prior to posting here, I DID search for aftermarket replacement packs. The best price I was able to find was $65 per pack. That isn’t terrible, but I like to have at least 3 on hand for multiple tools plus a spare, so I’m looking at $200 plus shipping for 3 packs. (nevermind the fact that the packs I was able to find had very mixed reviews)

In my mind that’s not a wise investment in a 10 year old set of tools when I could upgrade to new brushless technology and brand new batteries for $300-450 depending on what tools are included.(granted replacing my entire set would be even more expensive, as it includes 5 bare tools)

Based on your suggestions; (and the fact that my packs in their current state are basically worthless) I am planning on attempting to rebuild my packs with brand new high drain cells, using Barkuti’s suggestion of low temp soldering and the materials he has linked. I figure I’ll start with one, and if I am successful, do the rest.

As with most projects, I should’ve addressed this issue much sooner, due to the fact that I am in the middle of doing the electrical portion of a sizeable addition to my home, and it would be really nice to not have to load batteries in the charger on such a regular basis. :person_facepalming:

For illustrative purposes:

I re-built that pack a year and half ago using solder wick. I used tape for extra insulation during soldering, to make sure the wraps wouldn't get damaged. It ended up being unnecessary. The flux, being liquid and pretty fluid, gets under the wraps and causes some superficial oxidation on the cells. Despite I cleaned them before rewrapping, some rust remnants can still be seen. If I were to dismantle the pack again, I'm pretty sure a nice bunch of additional rust pecks would be seen due to my second flux application to rebuild the pack. It is completely inconsequential, though.

this was the thread that I first saw it on:

I built up a 10S4P bike battery using that approach (I have pics but I’m too lazy to find a pic hosting website to post them) and then tore it back down again to sell the cells when I realised the battery didn’t work (long story). Took ALOT of effort to pull up those strips. Basic idea is that the nickel to battery terminal spot weld blows through the thin copper and pins it in place between the two.

I made a couple of 18V li-ion battery packs using the old crappy Sanyo GA cells from my bike battery using that approach. One used a “50A” BMS and balance board, which runs my drills and lower draw stuff fine, but shuts down on my hand vacuum and leaf blower. The second one is just batteries, no BMS, and is just fine - used it at the weekend to clean up the yard. Does have some sag with the leaf blower, but that’s the shitty old cells, not the connections.

Is it oversized enough?

And after pack it better