This one is for those of us modding where a 7.2V pack just won't fit. Wish you ever had a pack that was a different shape? I'll start with a common 7.2V pack. Got it from Radio Shack but it is pretty common. This technique shows the particular shape I needed but you can configure as needed.

Part 1

Step one, use a hobby knife to cut away the heat shrink tubing. You will find that the pack becomes quite flexible. Upon inspection, you will see that the cells have a small strip of Nickle spot welded to either side. This is done because it is easy to solder to. You can use wire cutters to cut the Nickle where needed.

Part 2.

Next you will need some heavy wire. I used 12 Ga multi-strand. Apply a large amount of solder to this wire as shown. Also 'pre-tin' the Nickle tabs with a generous amount of solder. THis is helpful because you don't want to heat the batteries too much during soldering.
Arrange the batteries into the desired shape and hold them together with black electrical tape. Solder the wire jumpers as shown.
When complete, wrap the pack with tape to keep things secure. Reaaply heat shrink tubing over the pack for integrity. I did not have any on hand and will do this later.

A little safety,
1. Make sure not to overheat the batteries during soldering
2. Remember they are hot. I had a spark occur when I shorted the pack with my wire cutters at one point
3. Remember your polarity when assembling. Most batteries are marked so this should not be a problem.
4. Test your pack after assembly before charging, should read between 7 and 9 volts when completed
5. Your soldered jumpers may have sharp edges. Do not let them poke through your tape or heat shrink. a card board sheet can always be inserted. Remember, this is a tank and should vibrate and go through some tough handling.
Hope this helps,
Perry

Thanks for posting, I was always a bit imtimidated by soldering batteries. Now I know, If you can do it, ANYBODY can! Just kidding!!

I started of by shooting BB's at them, then I tried to eat them, then I realized a soldering iron would work.