Even though I knew I was getting the Vader FX saber for xmas, I couldn't help checking the demo model of it and the Luke FX saber down at the local Sharper Image during some unrelated holiday shopping. The Vader saber had enough batteries to light up and make its correct sounds, albeit a tad dimly and quietly, but the Luke saber's batteries were apparently weaker as the sounds were badly garbled and the saber was rapidly blinking on and off - this didn't stop people from dueling with them though, as soon as I was done checking them out, some folks came by and started to hack at each other.
So here's where the strange comes in... the luke saber's blade - which is EL material (a thin paper-type stuff that glows when powered, the Indiglo stuff in wristwatches) surrounded by the plastic tube - had a couple holes in the EL around the middle of the saber, jagged little breaks, the largest one being about an inch in diameter. What I found odd was that these breaks didn't affect the rest of the EL around it at all, it continued to light up as normal even though part of it was missing. If this was a standard circuit, the breaks would cause the lights above it to go inactive, but that's not how it works I guess.
Anyway, this is a good reason why you shouldn't duel with your FX sabers, as nothing could be sadder than a lightsaber with a hole in the middle of the blade.