how do i do this?

If you have trouble with the rosin core solder ... I've found that acid core (plumbing) solder works well for soldering to the large, flat NiCad battery case area. I know that purists will reply here that acid core flux is not desirable for electronic applications due to the fact that the acid is corrosive. But I'd ask these people to keep in mind that most batteries will only last a few years so a 40-year life is not essential in this application. So, if you can't get the solder to hold to the case with rosin flux, try cleaning the area and using acid flux instead. Also, minimize the time that the soldering iron is in contact with the case so you do not damage the new battery and as suggested, use a well tinned iron.

Bob

Your local Batteries Plus will spot-weld a pair of solder tabs onto a NiCd cell for about $1.

It's generally not advisable to solder directly to nicad batteries. If you do it, you want a real hot soldering iron and prep the surface well first so the heat can be on it as short a time as possible but unless it has tabs I don't recommend it.

I've been making up battery packs for some of the Sony "Micro" radios lately and agree with what James says. After having a maybe 50% success rate soldering directly to the battery, I now have my local "Battery World" put tags on the individual cells - they do the neatest spot welding ever. Well worth the extra few pennies. BTW, MiMH cells are usually available in the same physical size as the NiCads, they have a little extra capacity, don't have as drastic a "memory" as the NiCads and do have the same voltage. Worth looking at. Works for me, YMMV.

Haggis.

... in fact, it's more likely to be too puny, leading to you sitting there trying to solder it for 30 seconds, cooking the battery in the process.

A nice BIG iron, used QUICKLY is much preferable to a tiddly little "safety" iron :)

--snip--

At the hardware store, you can find a little "kit" (plastic bubble on a cardboard backing) put out by Alpha solder (I think) that is a piece of solid-core solder wrapped around a tube of flux. The stuff is advertised for "non-electrical repairs", and mentions stainless steel. Makes it easy to attach wires to NiCd cases. They make several of those kits, for various uses; make sure you get the right one.

The flux is as runny as water, so *watch out*. Saturate a cotton swab with the stuff, kind of "scrub" it onto the cell, and tin quickly with the supplied solder and a hot, clean iron (I use a 100 watt gun). After it's tinned, you can attach the wires using regular electronic solder.

No relationship, just a happy customer.

Isaac