On Tue, 8 Mar 2011 18:34:44 -0800, "William Sommerwerck"
wrote:

The actual problem was not an intermittent switch. It was the last thing I'd
have expected -- one of the welds on the battery pack had come loose!

It happens. Spot welding takes practice.

Without turning this into a megillah... Any suggestions on repairing it
without damaging the cell? I don't have welding equipment. I do have an
EDSYN pencil iron, and a 100W RadioShack gun.

Test the broken flat wire to see if it can be soldered. Keep the
battery as cold as possible (i.e. wet sponge). Plenty of liquid flux
and heat. Work fast to keep the heat affected zone to a minimum.

Please don't turn a straightforward question into a tsimmes. (But you will.)

Mazel Tov. You can also build your own spot welder with a big fat
cazapitor. Search Google and YouTube for "capacitor discharge spot
welder". For example:
http://forum.allaboutcircuits.com/showthread.php?t=24385
If you don't want to build the entire circuit, just charge up the
biggest capacitor bank you can throw together. One lead goes to the
battery terminal. The flat wire goes is placed on top of the
terminal. The electrode is some kind of heavy (#10 awg) solid copper
wire. Compress this sandwich together, and apply power at the
capacitor bank. Hopefully, it will weld the flat wire, and not the
capacitor terminals. In theory, the stainless leads with have a
higher resistance than the copper electrodes, so the stainless will
heat up, not the copper.

Last resort is to drag it down to Batteries Plus or some similar
vendor that has the proper spot welder.

Very last resort is to just slop some epoxy on the flat wire and
battery terminal, and hope that it holds.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS