How to solder 18650 Li-Ion batteries

[@mariondavisjr.5791]

A fantastic and informative demonstration that was in no way diminished by shaky hands. Thank you for sharing your skills with us. The tip on using the heat compensating soldering iron is great advice in itself.

[@gordyallan4385]

Excellent video on soldering takes me back to my days in collage when I was 17 learning how to solder. I use a green or brown scouring pad to clean the excess oxidation on cells its not as abrasive. A trade trick get some blue tack and stick your wires on them and stick them to the bench. Its a cheep second or third hand as you will need them while soldering connectors. Hotglue does to keep your cells together. I also find if you get a good quality manufactured pcb the solder will not come off the board. To get the solder off without damaging the pcb mix the solder on the board with your lead/tin solder and use a solder sucker to remove the solder done by the manufacturing process. I would also recommend using pcb cleaner or isopropanol alcohol to clean the pcb before and after removing components. Makes a professional job. Get it from RS, CPC or you local electronics supplier.

[@navigator902]

Genius.... learn every time when answering the bell Helps my mental health using your philosophy sense of humor is how I get by as well, and patience w/ my hands while I work.

[@DanWA]

Thank you for all of your videos and advice Bruce, the legacy many older people are leaving through youtube videos will hopefully live on for multiple generations and provide inspiration and education to many.

[@woodrunner51]

Just like proffesors on my college (the older they are the better they are) you make the best educational videos, talking about the basic details needed to understand the whole picture
Thank you sir!

[@wdavie27]

This worked 100% for me Bruce I made 2x 2s packs for my petrol baja buggy and only used one pack my buggy runs for 3-5 hours every day for a week on one charge \m/ great idea

[@gamerharmeet]

Thanks.
I had just 3 cells to solder.
There was no point investing in a spot welder. With your tutorial I feel confident.

[@MrCroky123]

Noob here. I'll look into your tutorials. That's some amazing job. Well done !

[@ironfront9573]

This is very helpful, and I appreciate you doing the demo regardless of shaky hands.
The amount of obsession over spot welders I'm every other video and discussion convinced me that lithium batteries are altogether incompatible with soldering.

[@terrylay]

PS Bruce all the best for your health, you kept me sane in my model building through the years

[@jaysonrees738]

Once again, you've proven to be one of the best teachers in the hobby. Going to be putting together some packs out of 21700 cells for endurance flight. Molicel is producing cells with incredible current capabilities.

[@joseico90]

I use the same method with the addition of using a little damp sponge to absorb heat off the cell solder spot at the end

[@silentskystudios]

Thanks so much for the suggestion to scuff the ends of the new batteries! My wife has a 16-volt CHV1410L Black and Decker hand vacuum that's several years old and would only run for a minute or so on a full charge. I ordered new 18650 li-ion batteries to replace the originals, but when I tried to solder in the new batteries, the solder would cling to itself in a ball and didn't want to melt to the ends of the batteries. I watched this video, followed your suggestion to scuff the battery ends with sandpaper, and it worked like a charm! Now the hand vac is back up and running!

[@chrissscottt]

Excellent vid, thanks fellow kiwi. I hope you're still teaching somewhere other than here, you're a fine teacher.

[@Hyprmtr]

Leaded solder has great capillary action.

[@unnamedchannel1237]

I also like caterpillars as well

[@Boz1211111]

capillary action depends more on flux type used, helpful thing i used to stop messing with expensive alloys and just buy a decent flux

[@pabloricardodetarragon2649]

@@Boz1211111 True. A good alcohol rosin flux is largely enough.

[@DocLarsen44]

Thank you very much, Bruce. My wife got me forever (lol) radio/flashlight, which has a hand crank dynamo, a solar cell and a wall blister for recharging. I know the storage system will not last forever, so I opened it up and discovered a 18650 inside with soldered on wires. I was concerned about replacing it when it will no longer hold a charge, but, thanks to you, good sir, I am no longer concerned. I live dangerously and buy 10 to 12 battery lots with reverse polarity protection from China. I assume 1-3 of them will be bad, but the price is low enough to make that acceptable. If they work on first charge, they seem work very well so far and I am only using them in flashlights, so far.

[@santiagoberto7178]

Thanks a lot for this. Ill go to the soldering tutorial as soon as i can, but you already gave me solution for some mistakes i have been making.

[@memadmax69]

Excellent video.
Probably the most important part is the sandpapering of the surface.

[@HowardBaileyMusic]

Thanks for this. I am about to replace the 18650 in a cordless screwdriver. Also I've been looking for a good soldering tutorial. I'm looking forward to watching that now.

[@licensetodrive9930]

I saw a video this year of someone who has soldered a ton of 18650s, he used fuse wire to solder them together, which I thought was a bloody genius idea, because if something goes wrong and wires get shorted out, the fuse wire just breaks.

[@DoctorWhom]

very thin wire? I just disassembled a NIMH pack from a cordless phone that used some fuse wire internally.

[@licensetodrive9930]

I bought some fuse wire with the idea of using it in this way one day, the 5A is thinner than you might think at 0.22mm diameter, whilst the 15A is 0.52mm and the 30A 0.78mm.

[@sulphur_fpv]

Never knew oxidization was not an actual word lol, learn something new everyday 😄. Thanks Bruce, great tutorial 👍👍

[@basebilljr07]

I did this about a year ago I made A 2S pack with balance charger leads for my fatsharks They were higher Mah batteries then any lipo i could find for it . I even wired in a little voltage checker with the 4 led's like original fatshark batteries have.they are still working great haven't had any issues with the solder joints.

[@keithlg420]

Best video I've seen and then you leave me hanging at the exact spot I really needed to see. How to join them together

[@hockeyguy820]

Contrary to what Bruce said, 18650 Li-Ion cells (and all other cylindrical cells with the same chemistry) have pretty well the same voltage range as LiPo cells. You can use the same charger. Charge to 4.2V per cell using constant current followed by constant voltage. Never discharge below 3V per cell. Li-Ion may be a bit more forgiving than LiPo for discharge but not significantly so. For Lipo cells I would recommend not going below 3.3V per cell, but 3V is not so bad. Optimal storage voltage is also about the same for Li-Ion at 3.8 to 3.85V per cell, not the 3.46V that Bruce mentioned. There are many sources you can look up to confirm what I am saying. I suspect that Bruce may have been thinking about LiFe cells, which do have a significantly lower voltage range of 3.6 to 2.5 volts per cell.

[@xjet]

If you look at the discharge curves for the 18650 cells you'll see that most of them rate the minimum cut-off voltage at about 2.5V... quite a bit lower than the safe minimum for Lipos.

[@slipperysebastian]

Yes I've been wanting a video like this!! Thanks Bruce

[@peterwilson5528]

You have a delicate touch with solder my friend. Thanks for the video :)

[@psygn0sis]

For some reason after clicking the thumbnail I thought this was a EEVblog video. I was thoroughly confused when your music started.

[@EvenTheDogAgrees]

Lol, same here, except I was expecting a GreatScott video. ;)

[@taylorquimby4004]

Look at those skills! I could never get a soldering iron that close to my finger without burning myself 😳🤣😅 great job and thanks for the info!

[@victoralcocer3926]

Thanks Bruce for sharing. You make it look so easy. I definitely need a soldering station.

[@tinkmarshino]

I use a soldering acid and wash it off after you have laid the solder down. That looks good.. But I will probably stay with the soldering acid.. I have used it for many years on many different applications.. But yours is a much safer way to do it.. especially if folks have not used acid before.. Now I may have to go try it.. I am a bit older myself (68 next may) and it would be a better way if I didn't have the acid in my tight little bench area.. so thanks for the "update"...

[@robertzeman4301]

Spotwelder was invented for mass productions and its has nothing to do with quality, its simply good enough to sell it. Repair shops and workshops with batteries seen many times a lot of cases when the spot from welding didnt survive the stress and peeled off. Soldering is much more better with higher quality and safety, but you have to learn how to do it and you can do mistakes. Btw you can also quickly tip the spot on the battery with the iron like a drummer. :)

[@NINJA2da]

Parkinsons or essential tremors is such a b'ch. I empathize, my father has Parkins. Great job, brother. I really enjoyed video

[@victoryfirst2878]

Thank you for lesson on soldering batteries Sir. Now I know !! How about using the 95/5 tin antimony alloy Sir ?? Nice soldering job fella too. 😀😀😀😀😀😀

[@CD-rt8wj]

you're the man bruce! Going to make a portable phone bank with these tips, I've got tons of old laptop cells around

[@pdrg]

Thanks for the confidence that it'll be OK - I've been a hobbyist off and on for decades but always been wary of soldering Lithium chemistry cells thanks to scary youtube vids, but yep I can keep it quick I'm sure, and your tip about not fluxing the cell pad is helpful

[@markkennard861]

Please don't under estimate the importance of extracting the fumes when soldering. Iv been soldering the 18650 cells for years and iv developed a blood condition called LCH which is being treated with chemo.. not fun..

[@robertzeman4301]

Damn, I hope you will do better and beat it. Thanks for the information. I was worried about this risk but I never know its actually as much dangerous as this case. Do you think its necesery to filter the fumes or just a normal fan is good enough?

[@558vulcanxh]

Thank you I've been soldering all my life but didn't know that (age 77) 🤔

[@markkennard861]

@@robertzeman4301 Hi. Yes all good now thanks. Depends on how much soldering you do. If its a small room then id ensure that the fumes are sucked out. A shed of garage you can just open the door i guess. A small fan that blows fumes away from your head is probably a good idea. Sill not 100% sure as the resin is from a tree I believe so there's only the lead content to think about. More research needed. Sorry it took 3 years to reply. :)

[@markkennard861]

@@araaraara12 Hi. Depends on how much you do. I was soldering all day. Think expelling air from the room using fan and ducting is all you need. Ventilation is the key.

[@dunworx3758]

Your a legend

[@dougmcpheters1546]

Excellent Bruce!

[@slickillaz316RCB]

I just bought these batteries for an rc car for longer run time but the positive end was too flat to meet connection this video explained exactly what needs to be done.

[@AddyOverbeeke]

In the aerospace industry, we are concerned for all tin solder as it can cause a condition called tin-whiskers. The tin grows tin crystal structure hairs (whiskers) and can cause boards to fail due to shorting. NASA has updated requirements restricting all tin solder. It's best when alloyed with lead. Just some fun trivia I am sharing from my job before I retired.

[@pulesjet]

Yes, Use a seriously Hot Iron. As soon as the solder flows, GET Off the cell. Limit the solder to just enough to wet the surface of the cell. Pre Tin the Wire and Re-flow connecting to the cell. Job Done ! Zero damage to the cell using this method. Use regular 60/40 solder.

[@adairjanney7109]

i think its good to have a piece of metal around in case it takes longer and heats up and use as heatsink to cool off where you soldered faster

[@Amir-de8xx]

Super informative video - just what I was looking for. Thanks very much for making this! Only thing is that I was so tense watching you solder so close to your hands without gloves on, haha.

[@sergeantcrow]

The word for the day is... 'blob'. Thanks for the excellent tuition...

[@ivanurban2383]

THANK YOU SO MUCH!!!! i was upgrading my drill with lithium and i didnt have a spot welder but THANK YOU!!!!
you get a sub and like!!

[@TheInfomoinul]

You are the true Master ....

[@daftnord4957]

You should look into hyperbaric chamber therapy. It forces oxygen through your skin and directly into cells, helps with so many things including the shakes

[@pnwRC.]

EXCELLENT video! This explains why the NMH battery packs I soldered together are having conductivity issues in the packs.

[@dextersxxxxlab]

Last week I made a spotwelder after watching a youtube video. Just need a momentary switch and a starter relais of a car or motorcycle, some installation wire for 240volt, two copper pins, a clamping block , car battery clamps and an old car battery. Last one I had so total costs are 11 euro or so. Works perfect. Just hold the pointy copper pins on the nikkel strip and push firm. And tap the switch real fast. A voila, two perfect spotwelds between the nickel strip and the battery.

[@jamesellis5445]

Great tip Bruce, I personally use a high wattage non temp adjustable iron and as you say, for a very small amount of time...I think the main distinction between Lipo's and Li-ion's is that the available current is limited in Li-ion's compared to Lipo's eg. 10 C compared to say 50 C to 100 C for Lipo's.

[@superdau]

The often used distinction between Li-ion and Li-polymer has nothing to do with chemistry (it is used wrongly. Pouch and cylindrical cells are just different form factors. There are different chemistries within that class, but again that doesn't have anthing to do with the form factor. The main difference is that the different form factors are built for different applications (high current vs. high energy density). They are *all* Li-ion batteries.
The formfactors can have different chemistry, but so can cylindrical cells between them and pouch cells between them. The form factor is not what dictates the chemistry, what the manufacturer puts in them is. You can have the same chemistry in either form factor. Have you ever seen something like IMR, INR, ICR, IFR, LMO, NMC, NCA, NCO, LCO or LFP written on cylindrical cells or in their datasheet? Those signify different chemistries. Pouch cells use the same, although they mostly use the Lithium-cobalt-oxide chemistry (ICR/LCO).
Real Li-polymer batteries are still a research topic. Those batteries are *still Li-ion batteries* , but their electrolyte is a solid polymer. Current batteries have a solvent based electrolyte and the only polymer in them is the separating plastic foil in the battery. It is that solvent based electrolyte burning btw. that you see in battery fires. Lithium has nothing to do with those fires.

[@jamesellis5445]

@superdau Thank you for such clarity on the topic, however I did not assert that the distinction was down to chemistry. All of this information I already know, being that I have a materials science background and I feel assumptions may have been drawn here. I was merely stating in laymans terms, that the different types of cells, have very different discharge characteristics. Furthermore I do appreciate this info is of a good understanding and valuable to new entrants to the hobby and our modern world in general.

[@MCsCreations]

Great tips, Bruce! Thanks a lot! 😊

[@markhinchcliffe5803]

How are you Mc,do you know much about the spot welders?

[@MCsCreations]

@@markhinchcliffe5803 I'm fine, my friend. Thanks! What about you? 😊
Well, I know they're better for the 18650 cells... I even know how to make one... But I still don't have one. 😕
Why?

[@markhinchcliffe5803]

Im looking at buying 1 for Christmas, but i know there are some that dont really do the job,i would like 1 that ticks all the boxes at a reasonable cost as well.
Oh im great to,thanks for asking

[@MCsCreations]

@@markhinchcliffe5803 Hmmm... I see... That's a difficult subject, really. 😕
What I would do is to look for reviews on UA-cam. Then I would look for complaints on Google. You know?
There's no much other way. 😕

[@markhinchcliffe5803]

Sunkko 787+
I did exactly what you just said,this unit seems to get a good wrap and has a good cost as well,there are a lot of bad units out there as well,they also mention to put it on a larger circuit breaker.

[@JNPhotography]

Thanks, been paranoid about doing this replacing cells in a battery pack (for a Hoover lol), much appreciated!

[@deepdivevr7244]

short answer is carefully.....i use a bit of wet cloth to wrap around the battery while soldering....also use sandpaper on contacts just before applying flux and 400 degree for the iron.

[@grumpyjohntxredneckrc6346]

A Tiny Drop Of Water Diluted Real Pine Tree Resin In A Dropper Bottle Works Best On Soldering Any Electronics! Won't Hurt Any Circuits & Is Actually A Great Protective Coating Against Corrosions!

[@JMathieson]

Nice work Bruce and good idea using the 18650

[@atomicskull6405]

A bit of flux such as Kester 186 will also help. Also Samsung 35Es are probably the best 18650 cells for RC transmitters right now. They have a slightly higher cutoff voltage of 2.65v rather than 2.5v and because the capacity is rated by 4.2v to cutoff you get a bit more useful runtime out of them. The flip side is that they have a lower max amp rating than Sanyo and LG 3500mah cells and a bit worse capacity at higher amps but for a low draw application like an RC transmitter this doesn't matter.

[@davidbarker3591]

I like the Alpha Fry 63/37 rosin core solder and Alpha Fry rosin flux. Never, ever have a problem soldering to the nickel strips or the batteries...

[@Brunmed]

I want to thank you sir, I'm now on my way to try this, carefully of course!

[@lasersbee]

Did that for my FPV goggles power.
6:55... A suggestion... Find something that you can fit the Battery into to hold it steady while soldering. Bruce... the hole in the Solder Roll itself comes to mind ;-). You could also drill a ~19mm/3/4" hole into some scrap 2 x 4 lumber to hold them steady. 10:18... Just saw that you found the battery holder trick... LOL

[@ZeroMass]

Use your biggest soldering tip ie the most mass, crank the temp and be fast. May also want to practice on dead cells first.. Quick refresher for the experienced, a good idea for the noobs 🤞👀

[@peterzingler6221]

Don't forget to clean and grease the solderd poles otherwise they will rust in a short amount of time.

[@jeffcotton526]

63-37 solder flows quicker and easier, plus it cools quicker preventing "cold joints" or gray and dull looking joints.

[@kevalinopicks5555]

Tell you what Bruce - you can solder way better than me even with your shaky hands! Good tutorial. I thought li-ion batts had to be tacked.

[@ZeroMass]

Its not the top you have to worry about as much as the bottom. The top is a raised thin piece on most cells. Also use 99% alcohol or acetone after you sand..

[@bamlani]

You made my day. Thank you

[@boactech3076]

I already did this with Samsung cells of Banggood. They are pretty good. Used 2 of them with a power level print with LEDs and a button to check for my skyzone goggles 👍

[@Bianchi77]

Nice video, well done, thank you for letting us know :)

[@mickspencer4171]

Nice one, thanks for sharing that.

[@handendaer]

If u dont have that good of a Iron i think welding (just with a better even) is better cus of The heat issues that can come with the welder if u need apply heat for a long time.

[@minibigs5259]

Ohhh, bench!
Welcome back to the bench! :o)

[@GENESUTUBE69]

fyi 63/37 solder has a narrow fluid to solid state so less chance of crystallization if there is any movment here at motorola we do not use 60/40

[@dunworx3758]

i was thinking you should make something like a set up with a weather balloon into space. And then you FPV back down in a glider or something like that.

[@lauriebot3941]

David Windestal did that a few years ago, it's worth a watch ua-cam.com/video/rpBnurznFio/v-deo.html

[@power-max]

hey Bruce! Just to be clear there isn't much difference between "lithium polymer" batteries and the "lithium ion" cells. Both are the same, but there are different chemistries which DO have some small differences (IMR, INR, etc.) The hobby has come to calling all flat pouch cells "LiPos"

[@power-max]

a d following that, the reason high power density pouch cells have a higher cutoff voltage is due to the higher discharge rate and safety margins. Cells have very low capacity when almost fully depleted. (voltage drops off fast!)

[@waynerussell6401]

Some of those chemistries are going to radically change life particularly transport.
The recent open sourced bench mark battery design from Tesla's Dr Dahn will allow many more cycles and be more temperature tolerant. Other electrolyte chemistries and electrode construction will allow quicker and higher voltage charging and increased energy density. Watch out for Tesla's Battery Day Q1 2020 presentation for the Dahn dual chemistry electrolyte and Maxwell dry process cathode LiIon 2170 cells.
jes.ecsdl.org/content/166/13/A3031.full

[@FPVREVIEWS]

Statement about charging is false. They can be charged to 4.2v per cell, just like a lipo. it's the discharge that is a lower voltage.

[@RCModelReviews]

Yes, I meant that the operational voltage works out to be lower over the discharge of the battery.

[@FPVREVIEWS]

@@RCModelReviews True, the average voltage is lower, because of the lower bottom range. Need some advanced calculus to calculate the watt hours in a discharge curve, rather than just looking at the MAH. This is why some people are confused as to their testing results, although they still stack up well against lipos in relatively low discharge rate applications. I prefer the NCR18650GA cells myself, if you can tolerate only 10 amps per cell max continuous discharge rate. They have 3500mah compared to the LGH2 cell's 3000mah, but the LG cells put out double the amps on demand, and that's more suitable for most people who don't know how to use a throttle, or think that airplanes are helicopters.

[@garyrobinson312]

very informative as always - but would just like to point out that care needs to be taken not to damage the plastic wraps on these batteries and if they do get damaged they need to be re-wrapped

[@MrSummitville]

And the plastic insulator located under the negative (-) terminal ...

[@DrDiff952]

You have showed soldering wires to cells. What about the connection on the other end of the cell? Or soldering the two cells together?

[@gmivisualsjason3729]

Thank you

[@999wilf999]

I solder for a living. I miss lead. Lead was great!

[@MrSummitville]

You can still us 60/40 tin-lead for for electronics.

[@Aviation437]

Great guide and with a sense of humor :)

[@theuglycamel8122]

Excellent again Bruce!

[@badmofo350]

Hope you're going ok Bruce. I don't watch your vids much anymore but I always really enjoyed watching in years past. I learned a lot from you. Do you have any idea what happened with the Spoktra50 channel? Those guys cracked me up!

[@greenscreenproductions2459]

Built a 2S 2P 18650 pack for my 3m glider using the same techniques. a high powered soldering iron or soldering gun is really essential for the task. I use a big battery pack in the nose instead of lead for ballast (which helps on those windy days). It also has the benefit of pretty much never needing to be recharged.

[@KillerSpud]

Whats the fun in soldering it when you could spend tones of time and effort trying to make a mini spot welder then giving up on the project all together later?

[@slybunda]

ahh the key to this is to scratch the surface of the battery where your applying solder. i been trying without scratching it and it just wouldnt stick. flux didnt do jack either. i think it must be some sort of anodizing on the terminal.

[@KingsPhotographySolutions]

Absolute legend. 😁👍
Thanks so much for uploading this video, both for the brilliant soldering advice, and more so for showing me that I don't need to worry as my shakes get worse over time. 🤗
(It was a real worry for me😔. 😅 At least untill seeing your amazing skills! Now I am hopeful that I too can keep going, and continue what I love to do for years to come. Thank you. 🤗😊)
If you've read this far (I tend to ramble😅 so) thanks for indulging me. Hope you all have a brilliant day, peace. 😁✌️

[@IanBeaty]

Great video and explanation. I had been wondering about this. Thank you!

[@markcollard9326]

Thank you very much for this video and info.

[@aaaaaaaaaassssssssdf]

the hakko 888d is pretty nice, sure the two button interface is garbage to set the temp but once you figure out that it's pretty nice and you are more certain about the temps

[@atomicskull6405]

Personalty I like the Xytronic LF-3200. It has 120W output and uses high frequency induction to heat the tip instead of a thermal element.

[@ewicky]

What temperature is your iron at? As important as speed is with Li-ion, I think many fellow viewers can relate to me: even with my iron on max, it doesn't go that fast.

[@TheSEMOMU]

I have a Samsung 18650 2S pack and my RC car don't work, finally I found the problem, cells don't have a good discharge rate and the voltage drop quickly, that active the battery protection cut off. I use the same pack for my transmitter without problems.

[@grumpyjohntxredneckrc6346]

You Need To Build 1S+2P or More Ps For Each S-Cells For Higher Draws With Li-Ions, Like Skate Boards, eBikes, Etc... Good Luck

[@xortig5415]

Thanks again Bruce for some super useful information. I hadn't looked into it and didn't realise that Li-Ion batteries were a higher energy density. I wonder if a boost converter is worth installing to lift the voltage?

[@bigdatapimp]

MXJO 18650s are the best you can buy.

[@pointedspider]

"It's terrible getting old, the body falls apart at great speed!"

[@ChuckPlains]

Haha, yep! It seems to be the only thing it does fast!!!! 🙄

[@Stambo59]

Hint, drill a hole in a block of wood to fit the battery to hold it still while you do this.
Leaves both hands free. :-)

[@jamesceastep8874]

Excellent hint on stabilizing batteries in a hole drilled in a block of wood! Thanks.

[@Pixeld.]

I want to say Thank You, I learned so much from your Videos!

[@TheMathMax]

thanks man! it worked!

[@arinasan247]

Thank you!

[@MetalGearMk3]

Do these Li-ion battery need to be balance during charging? What kind of charger would you use? I trying to figure out what's the safest way to charge such a battery pack.

[@grumpyjohntxredneckrc6346]

Yes The Same As LiPos, See My Comment On Here For Full Explanation... Thanks

[@ZebbMassiv]

Use a 100w-150w soldering tool for better quality results

[@jurez8752]

for the next chapter : how to solder lipo cells ?

[@cedriclynch]

Don't solder lipo cells! One of the tabs is made of aluminium, which can only be soldered with a special very corrosive flux that needs very high temperature to work. The heat sets off a chemical reaction in the cell, and a couple of days later most of your cells are inflated like balloons and no longer work. If you cannot spot-weld the tabs, make some small holes in them and bolt them with small nuts, bolts and washers. Also apply a product such as Noalox to the tabs when you bolt them, to maintain a low-resistance joint.

[@jurez8752]

@@cedriclynch ok , then the really good way is to spot weld them. thanks !

[@Bige4u]

Pro Tip... use liquid or paste flux, solder will flow and adhere more quickly to battery, then use at least 70% isopropyl alchol to clean afterwards, flux is a little corrosive.

[@Nabilphysics]

Shaky hands but steady output.