I am having a issue with my batteries. Im trying to make some saddle packs for my 10L. The issue im having is i cant get my solder to stick to the batteries. Is it that i have a crap iron? I figure even a cheap one would get hot enough. Im using flux like i thought i should. I don't want to over heat the batteries. What am i doing wrong?

Good day!

You will need a fairly hot soldering iron to do it, I would say no less than 80W.
Let the iron sit and get hot, do 1 conetion and let it sit again to regain its heat. Use thin solder with a rosin flux core.

remember to rough up the surface where you want the solder to be. use either some 320grit sandpaper, a sanding drum on a dremel or small jewelery flathead screw driver and scratch some crosshatch.

in terms of the soldering iron, use one with a big chisel head and about 70 to 80w should do it.

good luck

PS. make sure you melt some solder on the soldering tip first, that will help heat up the surface of the cell faster as the soft solder will take up the uneven space between the tip and the cell. if it's done correctly it should take no longer than 2 to 3 sec to heat up the cell to take in the solder and should flow nicely.

After you rough up the end of the cell, wipe it off with something like motor apray to remove anything thats not compatible with solder. I use a cutoff wheel on my dremel and make a light pass over the end of the cells to rough it up, then wire it clean with motor spray and a clean rag.

You prob should be using a separate rosin core compatible flux if the solder is not wetting the surface of the cell. That cleans and preps the surface for soldering, sometimes the flux in the solder is not enough. After cleaning, keep fingerprints of anything thats going to be soldered, the grease in fingerprints can mess things up. I use an 80watt Weller to put together or repair pacs, it does a good job.

Pre-tin the end of the cell and the batt bat, that way you'r en the cell for the minimum time possible with the heat. If you put too much heat into the cells, you can compromise performance.

So i take it the issue im having is that my 25 watt Iron isnt getting the job done. Looks like i need to go to the store. Thanks all.

That'd be my conclusion - don't think a 25watt iron is enough. The end of the cell is pulling the heat away from the iron faster than the 25watts can supply.

Absolutely right. A 25W iron will be nowhere NEAR hot enough to solder batteries, & in addition, you also need a fair amount of surface area in the tip so you can transfer that heat quickly & efficiently. That's one of the reasons why those 80W Wellers work, they have nice big & thick tips that allow for FAST heat transfer(the more area you can get the better, within reason, you do have to be sure you can control it, don't want the tip to touch anything else). And coupled with the other techniques mentioned(using some flux, scuffing up the surface of the cells, tinning everything, etc.), it should make the soldering go a LOT quicker, which is the best thing for the cells. That's why many have damaged their cells when connecting them, with less heat & less iron surface area, they end up holding the iron on too long, & that heats up the cells' interior, risking damage.....