I solder them directly to each other.

Howz this accomplished, you ask.

First off, you'll need a 40 watt soldering iron. Weller makes one that sells for about $25 at your local hardware. If you're going to be an electric powered plane flyer you need one of these. Next get a hammerhead tip for it. You can buy these from Hobby Lobby for about $10. Also get some 60/40 rosin core solder.

Now, get yourself a 36" long hunk for 1/2" triangle stock. Cut it in half and glue together such that the halves make a Vee that the cells can rest in and line up.

Pin the triangle stock to your workbench and have some making tape on hand.

Take each cell and roughen up the ends slightly with a grinding wheel on your Dremel..... Be careful not to over do it here! Now clean each cell end with a little acetone or alcohol.

Get your iron hot and then tin (melt some solder) onto the ends of each cell. You wanna make sure the iron is hot for this because you want to get on the cell melt the solder and get off as fast as you can to avoid damaging the cells. Usually 5 seconds or less.

I like to do all the cells on one side and then flip them over and do the other sides in order to let them cool a little before I hit them with the heat again.

Now, take one of those cells and place in it the balsa Vee tray we made earlier. Use the mashing tape to hold it in place so it won't slide easily. Place another cell in the tray and check the polarity + end to - end is how we want to solder them.

Take that hammerhead soldering iron and hold it between the cells and slowly push them against the iron head making sure to contact each cell at about the same time. Watch for the solder to melt on both ends. Once it does, quickly remove the iron and slam the cells together. Hold for a second or two so the joint can cool and your done. Repeat the process as needed. You should wear glasses and a apron while doing this because a little solder usually splatters.

If you have some old cells lying around practice a little on them. If not, just be methodical and you'll be fine. It's not really very hard.

If you have any questions about what I wrote above please don't hesitate to ask. I'm not always as clear in what I describe as I'd like to think.

Wiz