Soldering Batteries

lxskllr

No Lifer
Nov 30, 2004
57,404
7,588
126
I had to fix a battery pack the other day. It had numerous cells wired in series, and some of the connections had come undone. I've seen it before, and it looks like the original connections were spot welded. How does that work? Anyway, I couldn't get a good connection on my solder joints. Seems like the battery dissipated the heat, and I couldn't get it hot enough for good flow.

I got them together, but it's the world's shittiest solder job. What do I need to do it right? A hotter iron, or perhaps a conductive epoxy? How do you guys do it?
 

sdifox

No Lifer
Sep 30, 2005
94,912
15,072
126
Machine spot weld, doubt you can do that manually safely. Just use a battery holder.
 

sdifox

No Lifer
Sep 30, 2005
94,912
15,072
126
I'd have to make my own. The cells are non-standard.

There is no such thing as non standard batteries, unless you have one of those lion polymer form fitted ones, which would not need soldering.

You could try heat shrink.
 

lxskllr

No Lifer
Nov 30, 2004
57,404
7,588
126
There is no such thing as non standard batteries, unless you have one of those lion polymer form fitted ones, which would not need soldering.

You could try heat shrink.

I need a holder that takes a 1.5V cell that's ~50% bigger than a AA, a flat top and bottom, and group them to make 12V. The whole thing needs to fit into a case with ~2mm extra space on all sides. Do they make such a holder? Or any holder that fits batteries you can't get at HomeDepot?

Would heat shrink give a tight connection?

Edit:
You mentioned machine welding. Is that something I can buy for a couple hundred dollars?
 
Last edited:

Rakehellion

Lifer
Jan 15, 2013
12,182
35
91
I need a holder that takes a 1.5V cell that's ~50% bigger than a AA, a flat top and bottom, and group them to make 12V. The whole thing needs to fit into a case with ~2mm extra space on all sides. Do they make such a holder? Or any holder that fits batteries you can't get at HomeDepot?

That's a standard size. Check sites like digikey.

Don't solder batteries. They'll explode.
 

jaedaliu

Platinum Member
Feb 25, 2005
2,670
1
81
That's a standard size. Check sites like digikey.

Don't solder batteries. They'll explode.

Amateurs solder batteries all the time.

Are you using flux? Are you using a big-ass iron and working quickly?

and make sure you clean the flux afterwards.
 

Brian Stirling

Diamond Member
Feb 7, 2010
4,000
2
0
Amateurs solder batteries all the time.

Are you using flux? Are you using a big-ass iron and working quickly?

and make sure you clean the flux afterwards.

So long as the output of the pack is disconnected there should be no concern for shorting, but if disconnecting isn't feasible a butane powered soldering iron eliminate that as a problem. Clean the contact area and use flux. Notmally the best method for soldering is to dab a little solder on the iron tip and use that to improve thermal conduction. Then, place iron on joint and heat up BEFORE adding solder. The goal is to have the joint hot enough that when you touch the solder to the joint it flows quickly.

I can see there being a problem with this if the contacts are very short so that the battery suck up the heat limiting the temp of the contact. If that's the case you may have to rig a pack using a holder. They don't have to make it easy for you now do they...


Brian
 

jaedaliu

Platinum Member
Feb 25, 2005
2,670
1
81
Too much heat is bad for the battery. Youtube should have tutorials/how-tos.

This place sells loose cells and supplies or they can make a custom pack for you. I believe you can even talk with them over the phone. (note: site is down at the moment) http://www.cheapbatterypacks.com/Default.aspx

I used those guys for custom-assembled packs for an AIAA DBF competition!

One battery pack was long, so I received the battery packs in a large USPS flat rate shipping box. Inside the box were empty small and medium boxes as packing material. Ingenious!
 

Thebobo

Lifer
Jun 19, 2006
18,592
7,673
136
Yea I've soldered hundred of batteries here.

Need to clean battery if you have a dremel tool or the like, even sand paper clean ends.

Clean Iron tip, make sure Iron gets hot, tin iron tip,
Tin the ends of battery it should only take a couple of seconds. you want to get the solder to flow just right at the iron in the end you will have what looks like a little puddle.

If you are using wire tin the wire and then all you need is to touch the wire to the battery with you Iron for to sec to melt solder. Done!

IF battery to battery I still use Solder wick its like the braid in coaxial cable but works great since it flat
 

PottedMeat

Lifer
Apr 17, 2002
12,365
475
126
Yea I've soldered hundred of batteries here.

Need to clean battery if you have a dremel tool or the like, even sand paper clean ends.

Clean Iron tip, make sure Iron gets hot, tin iron tip,
Tin the ends of battery it should only take a couple of seconds. you want to get the solder to flow just right at the iron in the end you will have what looks like a little puddle.

If you are using wire tin the wire and then all you need is to touch the wire to the battery with you Iron for to sec to melt solder. Done!

IF battery to battery I still use Solder wick its like the braid in coaxial cable but works great since it flat

this - also use good old leaded solder
 

BikeJunkie

Golden Member
Oct 21, 2013
1,391
0
0
1. Hot iron (counter intuitive to some). The hotter the iron (within reason), the less time you need to apply heat.

2. Tin well. Apply a good flux to each component; make sure to only apply it where you want to solder to flow.

3. Mate the two components and apply heat. If you tinned properly and your iron is also properly tinned, you do not need to apply more solder.

#3 is where most people go very, very wrong IMO. They keep applying solder to pre-tinned components. Pre-tinned components already have all the solder that is necessary to join the parts.
 
Mar 10, 2005
14,647
2
0

Scarpozzi

Lifer
Jun 13, 2000
26,389
1,778
126
I used to solder 1.5volt AA NiCad batteries to replace drive-thru battery packs (McDonald's, Wendy's, and KFC) @ $28/each.

I used a high quality Weller & Tenma soldering iron at very high temps. I'd clean the surface with an alcohol swab, score the surface, and didn't hold the heat on the battery for very long. I actually melted the solder onto the end of the iron instead of the heating the surface to melt the solder.

Scoring the surface was key...I then used battery wrap and the wide part of the iron to cover the joint.
http://www.ebay.com/itm/like/221012316502?lpid=82
 

Jeff7

Lifer
Jan 4, 2001
41,599
19
81
Google for DIY battery tab spot weld.

Something there might be usable.


I'd read that soldering to rechargeables was not a good idea, as it can damage an internal seal at the terminal. Spot welding puts a very brief impulse into the tab right where it's needed in order to form the bond, and it's done before any damaging heating can occur.
 

WHAMPOM

Diamond Member
Feb 28, 2006
7,628
183
106
I had to fix a battery pack the other day. It had numerous cells wired in series, and some of the connections had come undone. I've seen it before, and it looks like the original connections were spot welded. How does that work? Anyway, I couldn't get a good connection on my solder joints. Seems like the battery dissipated the heat, and I couldn't get it hot enough for good flow.

I got them together, but it's the world's shittiest solder job. What do I need to do it right? A hotter iron, or perhaps a conductive epoxy? How do you guys do it?

Welding flux on both parts, tin both pieces first and use a large copper tipped iron for a fast heat. Do I need to mention sanding the parts nice and shiny first?
 

WHAMPOM

Diamond Member
Feb 28, 2006
7,628
183
106
TIP: properly cleaned and fluxed, solder just flows, even uphill If it beads up it's your fault.
 

lxskllr

No Lifer
Nov 30, 2004
57,404
7,588
126
Google for DIY battery tab spot weld.

Something there might be usable.


I'd read that soldering to rechargeables was not a good idea, as it can damage an internal seal at the terminal. Spot welding puts a very brief impulse into the tab right where it's needed in order to form the bond, and it's done before any damaging heating can occur.

Thanks for the tips everyone. My soldering technique could use some tweaking, and I think I'm due for a better iron. Long term, I like the idea of building a welder. This will be an ongoing project as batteries die, and it'll save significant money doing it myself, as well as being much more convenient. I currently have about eight packs that need rebuilding, so I'll have plenty of practice :^D
 

Red Squirrel

No Lifer
May 24, 2003
67,308
12,094
126
www.anyf.ca
You'll want to rough up the area and probably use flux. Use the hottest solder iron you've got but be sure you can make the solder joint in no more than a few seconds. Don't want to heat up the whole battery. Let it cool before doing the other side.

You could also use a rubber band to hold a foil paper contact tightly against the battery. Basically a crude holder.

Wear safety glasses. Just in case.