Using CAT5 cable as a Balance Lead extension

I have the need to make a 4' long extension for my 6S balance leads. Has anyone ever used CAT5 for such an extension? Would the small wire gauge (and associated voltage drop) be too small to perform the occasional rebalancing of cells?

That all depends on the load on the circuit. Assuming 24awg, 1A will have a 3.5% voltage drop, while .1A will have a .35% drop. The actual load will depend on the balancer you use. I would suspect the load is minimal, but you can determine that by measuring the resistance of the circuit. My balance leads are over a foot long using 26awg and they work fine. Meaning I haven't burned up a cell yet in almost 2 years of charging to 4.2V and I didn't go to the trouble of measuring the load. If your cat5 is 22awg, voltage drop will be ~33% less. For 4' extensions I'd use the largest wire within reason.

CAT 5 can have various AWGs. In its use for ethernet, it's carrying very tiny current. When you use it for balancing, it'll be carrying more.

Also, some cat5 is solid, some is stranded. That makes a difference to flexibility, if that's important to you.

Check the AWG of the cable you're about to use, and look up the load capacity here:

http://www.powerstream.com/Wire_Size.htm

I use cat5 to carry small current signals on my bike; I use it for the voltmeter, the ammeter and the 5 volt handlebar PDA supply; six wires in a small (and very cheap) cable, with a couple of spare wires that I'm sure I'll think of a purpose for one day.

I'm using 22AWG for my balance charging setup. 2 to 3 feet long depending on which charger I am using. I would use 22AWG or 20AWG if I were you.