Thanks, Timbo, Martin, Eric and Adam, for your help. Component-shop sem to have just what I want, 1/4 and 1/3 AAA cells at very reasonable prices. Can't see anything similar on Maplin or Overlander, and cordless phone packs all seem to be larger cells, but your 3.6v packs, Martin, sound about the right cell size. If you feel like selling me a few I can probably split one or two up and add cells to others to make 4.8 or 6v packs. Thanks, everyone. As a point of interest, for anyone who makes up their own packs, I see that John Emms on the Puffin website recommends soldered rather than spot-welded cell links, for minimum resistance. This is OK as long as you do the soldering quickly, to avoid overheating the cells, so I think you need the cell ends and the connecting strip pre-tinned, and an iron with good thermal capacity, so it doesn't cool off as soon as it contacts the cell. I was looking around for something to use for connecting strips, and hit on some copper plant labels, which should be available at any garden centre. Mine are .006 inch copper sheet, quite flexible and easily cut with scissors. Checking the resistance, I found that a strip about 1/8 inch wide and 1 inch long has a resistance of about 1 milli-ohm, which should be OK for low to medium currents, say up to 20 Amps. Above that, something a bit thicker might be advisable.