I recently assembled few 6 cell packs and found out it was very hard to get temperature on negatives. I used very high temperature (450 c) in order to finish soldering as quick as possible, the positives can be done within few seconds but more than 40 seconds for the negatives, that damaged the cells somehow I suppose. Is it because of different materials? is there any technique I can use to put solder on negatives quicker?

Are you using flux, and pre tinning the battery and bar?

You should also be "roughing up" the terminals and then cleaning them with something that doesn't leave any residue like motor spray or denat alcohol. Then its time for tinning and flux.

I use a dremel and cutting disc and very lightly make a pass over both + and - terminals - lightly so you can just see some abrasion. Motor spray and clean each as they go into soldering jig. Never have prob with anything not sticking or anything failing my pull on it test after soldering.

That's some good information right there. I've had the same problem, and would always get upset cause the solder joints look like crap!

I'll have to try that technique on my next pack and see how it does.

I've got some information from other forum. They told me to use higher watt soldering gun(higher than 80 W). It makes sense to use high watt because the negatives generally have larger surface so the heat will dissipate quicker. I think I will buy 100 watt soldering gun to see if it works. But one guy told me he can use 40W to solder cells. well I don't know how he did it

I use a butain (sp?) torch for all my soldering needs, and it does the job very well, and I know it heats upto 450deg F, but I'll have to try that trick listed above...

You also want to make sure your iron has a big chisel tip, tips that are smaller will loose heat faster, the bigger tip holds heat better. Also make sure to give the iron a few seconds to recover temperature between joints.

Using a higher wattage soldering iron makes it easier to make a mistake and damage the cells. A hotter iron means you have to work quicker, and if you don't know what you're doing you're asking for trouble.
I've been using a 40w iron for years and years and never had trouble putting together packs. But if you're not using flux and pre-tinning the cells and tabs before beginning I can see how you're having problems.

I use a weller 80watt, sp80l, with the large tip but I'm on and off the cell in less than a few sec, even if I don't get the job done (rarely) - come back to it later after it cools.

40sec on a cell is not good and most prob did damage the cells. Your prep or something is wrong, possible the lack of flux and or roughing/cleaning the cell terminals. Even grease from fingerprints can mess this up, its gotta be clean to start with!

My problem is I can get job done on positives of cells within few seconds (I didn't use flux because I had no problem on positive sides) whereas I cannot pretin on the negatives even I used flux. My solder iron is 60 watt and I used chisel tip. I have no problem on soldering on bars ,wires, positive sides of the cells(ni-mh sc 4600) but only on the negatives. I have no clue what's gone wrong, the only thing I can think about is my iron cannot efficiently put temperature on larger surface like negative side. Is there any tips you can share?

try wetting the tip with abit of solder before placing over the battery tabs.

it should conduct the heat better from soldering iron to the battery.

i am using a 60W soldering iron. never gave any problems

hope this helps

Wonder if those neg ends have something that was put on them? Maybe to help prevent accidental discharge? Its now a little late, but take a dremel or some fine grit sandpaper and clean the neg ends. Wipe the ends off with motor spray or denat alcohol.

When solder won't stick, there is usually something on that surface that is preventing the flux and solder from wetting that surface. Thats why you clean and abrade or rough up the ends of the cells and wipe them with a cleaner that doesn't leave any residue.

make sure that the tip of the iron is clean, if its black it will not melt the solder, you can use sandpaper or a file to clean it.

Save your money, a gun is USELESS because it doesn't transfer heat to the work area as efficiently as an iron. I've been soldering batteries for 20 some years using a 40W Weller (I'm on my third one but bought a Hakko 736 which is the best soldering station for the money).

The trick is to keep your iron's tip in good condition by cleaning it and tinning it regularly and often. Oxidation is the worst enemy of soldering and almost everyone that has problems soldering are using a buggered up tip. Radio Shack sells little tins of solder tip cleaner and tinning, these work, use them and you'll be a much better solderer.

The problem with doing that is that you are removing the plating from the tip which enhances heat transfer. Soon the tip will be useless and oxidize almost immediately.