# Soldering to batteries



## Praxis (Apr 30, 2007)

How does one solder to batteries that don't have tabs?

This is actually for refreshing a power tool battery pack, but I won't tell if you won't. I'm terrible at soldering (may have fried my lflex), but I know you're supposed to heat up both sides of the connection to the solder melting point. But for a tabless battery, this would damage the battery, right?

The original batteries didn't have tabs either for what it's worth.


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## pethelman (Feb 26, 2011)

Praxis said:


> How does one solder to batteries that don't have tabs?
> 
> This is actually for refreshing a power tool battery pack, but I won't tell if you won't. I'm terrible at soldering (may have fried my lflex), but I know you're supposed to heat up both sides of the connection to the solder melting point. But for a tabless battery, this would damage the battery, right?
> 
> The original batteries didn't have tabs either for what it's worth.


Yikes... you really don't want to try soldering directly to the anode/cathode. Just take them down to Batteries Plus and have some tabs spot welded on. Or better yet, they can even build a pack for you out of the cells that you have in any shape that you want, essentially duplicating the original form factor. Well worth the small cost.


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## VegasF6 (Jul 15, 2010)

Yes, to do this at home takes a pretty decent iron, experience and knowledge of battery safety and chemistry. It could be especially dangerous if this is any sort of lithium based battery but even for nickel chemistries you risk damaging the batteries. If you really want a project you could build your own capacitive discharge battery spot welder but somehow I doubt that's what you are looking to do 

A battery welder is the way to go, I didn't realize that Batteries Plus could do that for you though, that is really useful information!


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## thickfog (Oct 29, 2010)

Used to solder all of my expensive rc car batteries. It takes one hell of an iron to do it without getting a cold solder joint that fails quickly. 

It's not dangerous or destructive to the battery as long as you're fast. Don't overheat the battery. Easier said than done. 

Li batteries I've never soldered. Not sure I would try. 

If battery store can put some tabs on for you, it may well be worth it.


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## pethelman (Feb 26, 2011)

VegasF6 said:


> A battery welder is the way to go, I didn't realize that Batteries Plus could do that for you though, that is really useful information!


Well, I didn't know it either till we had a project at work that required a custom lithium pack, so at least our store in town has the capability, but I would imagine that most do. They literally welded up a 8 cell pack and shrink wrapped it while I watched, using off-the-shelf energizer lithiums. While we were talking, the guy mentioned that they're all the time building up custom packs for bike lighting systems for local guys, using whatever flavor of lithium cells that you might like. Definitely a nice resource.


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## DIYtailight (Sep 14, 2009)

thickfog said:


> Used to solder all of my expensive rc car batteries. It takes one hell of an iron to do it without getting a cold solder joint that fails quickly.
> 
> It's not dangerous or destructive to the battery as long as you're fast. Don't overheat the battery. Easier said than done.
> 
> ...


+1 I always soldered my nimh R/C car batteries with a 90W soldering gun. The first pack I totally screw up, and it seemed that no matter how much heat the solder wouldn't melt and fix the battery bar in place (the connecting piece of metal between cells). Anyway, so that pack was roasted, but still good enough for a couple years use on my old HID light.

A year ago I pulled some old cells out of a broken laptop's battery and tried soldering a 3S li-ion 18650 pack. Soldering worked well, though I never actually used the pack since I went with a 2S battery instead, but it was so quick to solder it on with the 90W iron that I would be very surprised if the cells had been damaged in any way. They likely didn't get hotter than a high rate charge.


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## brad72 (Jun 12, 2009)

I have soldered up several li-ion packs with no problems but I always tin the terminals with solder first before attaching any wires. 

I just make sure I scuff the ends of the cell with some fine emory tape, use a solder flux pen and apply some liquid flux, heat up my gas iron till nice and hot, clean the tip and tin with some solder then touch the tip on the battery terminal, apply solder and a few seconds later the job is done. 

Then it's just a case of taping the pack in the configuration you want, then solder some pre tinned wires to battery terminals that you tinned earlier. The battery barely gets warm if you do it right.


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## mattthemuppet (Jul 16, 2004)

pretty much as Brad said, I've done several packs and I've never had any problems. 3 of them are still going strong 2yrs later 

I used a file or dremel grinding wheel to lightly scuff the terminals. Then I tin the terminal (couple of seconds heat at most) and the wire. Every time I apply heat to the battery terminal I cool it down afterwards by holding a pair of pliers on it for 5-10s. Then hold the tinned wire to the terminal with that pair of pliers, heat until the solder melts and merges, cool with pliers. Shouldn't take you more than 1-2s a joint, even with a cheapy 40W iron. Make sure you hold the batteries in place securely so the only thing you have to hold are the pliers and iron.

Practice on your old cells first so you can figure it out and gain confidence. I'm going to be building a power tool battery pack for an old drill someone gave me, it'll be interesting to see how well it works!


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## Praxis (Apr 30, 2007)

mattthemuppet said:


> Then I tin the terminal (couple of seconds heat at most) and the wire. Every time I apply heat to the battery terminal I cool it down afterwards by holding a pair of pliers on it for 5-10s. Then hold the tinned wire to the terminal with that pair of pliers, heat until the solder melts and merges, cool with pliers.


Thanks for the detailed steps. Here's what I can't figure out, though--isn't the rest of the battery going to act as a heat sink and be cooling off the terminal? And whether or not that happens, isn't the plastic shrinkwrap on the battery going to melt near the terminal?

I'll definitely need a better iron. First I did everything with a gun(!) Then I overreacted and got a little 12W iron. Been meaning to get one of those little Hakkos. In fact....[click, click, done--I love Amazon.]


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## mattthemuppet (Jul 16, 2004)

no problem. The shrinkwrap won't melt and the rest of the battery shouldn't warm up because you're applying heat for such a short amount of time. If you can't make a good join in a couple of seconds, let it cool off and try again a minute or so later. Just don't hold the iron on longer in the hope of making that joint.

I used to use a crappy Radioshack 50W iron without problems, although my Hakko station is much more pleasant to use. Tinning, speed and cooling down the terminals afterwards are the key.


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## El34 (Jan 11, 2009)

I solder together 18650 battery packs all the time

Use a 40 watt or more iron
Scuff up battery ends a bit to make sure they are clean and the solder will stick
Tin the battery ends very quickly with a small pool of rosin core solder.
Tin your connectors where they will be attached to the battery

Solder the connector very quickly with a dab of solder.

Warning, Li-Ons don't like to get hot and if they have protected circuit boards you have to solder very quickly to avoid damaging them.

The secret is to get the hang of soldering quickly and getting away from the surface as fast as you can and still create a good solder joint.


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## Leopold Porkstacker (Apr 21, 2010)

I’ve done this before with 18650 Li-Ion batteries. As El34 mentioned, scuff the contact area first (rough sandpaper worked well for me, I believe 80 grit), and then solder… but I used some standard flux (the stuff that crystallizes in the container) and the leads soldered onto the batteries beautifully.


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## Praxis (Apr 30, 2007)

So, yeah--I was wrong; the existing batteries are welded I guess: 









Any hints for disassembly? Also, I was practicing on a dead Trustfire and couldn't get the terminal heated up enough. Roughed up the terminal, tinned the tip of the iron,, temperature 450-650° F. What am I doing wrong?


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## VegasF6 (Jul 15, 2010)

To disassemble, wire snips and kind of a twisting tugging motion. Be carefull not to cause shorts. You probably will and you will know it. I suggest doing it in the garage or somewhere you can throw them if it goes wrong. 

I hesitate to give advice soldering to lithium cells, you may cause damage that isn't immediately apparent. But I will say much higher temps, 800 to 900f and also a large chisel tip not a conical. Flux.


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## mattthemuppet (Jul 16, 2004)

hmm, I would be VERY _very_ careful about pulling the tabs off the +ve terminals (ones with the buttons) as you can easily damage the wrap and short the +ve terminal and body (-ve) of the cell.

(note, before doing anything, mark the tabs with the +/- using a sharpie or similar)

But, that being said, here's how I would do it: use a craft knife or jewellers flat tipped screwdriver and carefully pry up one edge of the tab. Then use a pair of needle nosed pliers to grab that bit of the tab and carefully roll the tab back on itself (like opening a tin of sardines, if you've ever done that). That will break the weld points with the minimum of force. You could always stick a bit of rubber under the pliers head to protect against shorts. By keeping the tabs intact, you'll make it easier to reassemble the pack.

As for problems getting solder onto the cell, as Vegas said, used a broad tip and high heat. I tin the tip of the iron with some solder first to get the heat to transfer fast then quickly feed the solder in. Remove quickly and quench. Good idea to practice on an old cell first (just make sure it's properly dead, ie. 0V, first )

What cells are you putting in there, IMR high drain cells?


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## [jsl] (Sep 20, 2007)

I have soldered a few LiIon and LiFePo4 packs and never had any issues. For smaller cells like 18650 my 80W Weller has been more than enough. For bigger cells, especially A123 cells that have a heat conducting aluminum shell under the plastic, you need a LOT bigger iron, I think I used 200W hammer-looking iron which worked well (with 80W all I could do was melt the plastic).

Welded tabs are not very easy to remove, from my experience. I have simply used wire cutters to cut the tabs.


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## Praxis (Apr 30, 2007)

Matt: Thanks for the warning. I'm not planning on reusing the old cells but I'm not fond of even old batteries combusting. I've got pictures noting the terminal placement. Having a decent camera always at hand (and using it) has saved me from *so many* problems.

The pack died pretty early. I'm actually replacing with these , but in retrospect the IMR high drain cells (available from the same vendor, even!) would have been a better choice.

From some googling, it's looking like the old pack was ICR (and quite possibly that's why it failed so quickly). Oh well, live and learn. Guess I could use the (unprotected) ones I bought elsewhere if I bought or built a protected holder, and then go try to find suitable replacements.


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## mattthemuppet (Jul 16, 2004)

well, live'n'learn  What's the tool? I'm pretty interested in the outcome as I have a nice Ryobi a friend gave me with a duff NiCd pack. I have enough salvaged good quality cells to rebuild it with li-ion cells, although I've really no idea if they'll be able to provide enough current. I have a 6S balance tap to put in and a little voltage monitor to experiment with though.


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## [jsl] (Sep 20, 2007)

I have used only LiFePo4 cells for tools. When replacing NiCd or NiMH cells, the voltages don't quite match but is slightly lower. I haven't found this to be an issue as they can provide a huge amount of current so the torque is more than enough. Lower voltage only means a slightly lower speed.

LiFePo4 cells don't have as high a capacity as LiIons, but still more than the NiCd or NiMH I have replaced with them. They are also lighter in weight, are not ruined if the voltage drops too low and can also be charged with huge amount of current, safely.


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## Praxis (Apr 30, 2007)

mattthemuppet said:


> well, live'n'learn  What's the tool? I'm pretty interested in the outcome as I have a nice Ryobi a friend gave me with a duff NiCd pack. I have enough salvaged good quality cells to rebuild it with li-ion cells, although I've really no idea if they'll be able to provide enough current. I have a 6S balance tap to put in and a little voltage monitor to experiment with though.


A combo set like this, although mine has a bit different set of tools.

Is it safe to simply swap Li-ion for NiCad? I would have thought that the charging circuitry would be different, and that the NiCad pack wouldn't have any protection to speak of.


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## christexan (Jun 1, 2004)

Regarding the picture of the pack above, a few notes:
1. If it "died early" it's a good chance one cell (or block of cells) in the pack died, but others are just fine. Happens a lot with serial/parallel combo packs from laptops, you'd think theywould have charge balancing considering the significant circuit boards in them, but they don't (at least not the Dell, Toshiba, or HP packs I've used). 

2. If you have welded packs like that, DON'T break the welds!!!!!!!! If you snip (I use tin snips, carefully, as mentioned shorting them even for a "tap" can lead to dark spots on your vision for a few minutes, or worse.
(Backing up here... put on goggles, cotton clothing, gloves, face mask, leather apron, hearing protection, do this outdoors and only if you are a certified Electrical Engineer with 20 years or more experience working on batteries!).... okay.. back to the story... VERY carefully snip the tabs (from your pic, I'd snip at each arm of the "T" right where the sides reach the middle or between 2 directly linked cells as appropriate). 

3. Now you have tabbed batteries, those tabs are actually SUPER easy to solder to in my experience. Scuff lightly, and solder to the (RAZOR SHARP, be careful) tab (I pre-tin, then solder pre-tinned wires as others have described above). When done, use pliers to carefully roll the tab up over the end of the battery, and squish it down if desired, etc to eliminate the sharp edges. This will solve both the cell heating problem, and the difficult soldering problem at once. (Still, solder fast so heat doesn't get a chance to wick down the tab, and cool appropriately with something immediately after soldering).


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## DeeEight (Jan 13, 2004)

Ya know... as to putting tabs onto cells... epoxy works well. You can get metal-epoxy that'll lock an aluminium tab to the end of a battery cell quite solidly with very little heat involved. Hell even crazy glue will do it in a pinch.


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## Praxis (Apr 30, 2007)

christexan said:


> 2. If you have welded packs like that, DON'T break the welds!!!!!!!!
> [...]
> 
> 3. Now you have tabbed batteries, those tabs are actually SUPER easy to solder to in my experience.
> [...]


Maybe I'm missing the point, but I'm not trying to preserve the tabs on the batteries to reuse the batteries, I'm trying to substitute different batteries.


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## Praxis (Apr 30, 2007)

Good news, bad news:

First, the old batteries have been liberated! More damage to the tabs than I would have liked, but oh well:










But, the batteries themselves look like there's no problem with them:










This was the case for every battery, 4.04 V +- .01V which is surely not the accuracy of this meter, but it works. I was totally expecting a bad cell, but...nothing. So, I guess the "charge a pack, it dies after 30 seconds" behaviour might not be the fault of the batteries.

I didn't think it was the charger, because although both packs I had weren't great, one was obviously worse. I guess it's something to do with the pack circuitry. Maybe some connection heating up and causing the heat cutoff to stop the charging? I'll have to look at the other pack more closely, measuring it after it comes off the charger.


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## Vancbiker (May 25, 2005)

You should test those under a load. The first time I salvaged cells from a dead laptop, they all were looking good. When tested with a load, one pair dropped voltage quickly.


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## mattthemuppet (Jul 16, 2004)

I agree with Vanc, resting voltage is no guide to the health of the cells (other than 0V = toasted). I even found a some Panasonic cells in an old pack that charged to 4.2V and kept that for weeks, but when I tested for capacity only stored ~200mAh


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## El34 (Jan 11, 2009)

yes, you have to run the batteries under load to figure out the batteries true condition


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