The pack on the string I got was fairly small--it's for two button-cells--but yeah, it's not negligible. I'm trying to get it to dangle from the clasp--the cord I'm putting the pendant on is pretty thick and stiff, so I can hide the wires underneath it. I've ordered a couple of different, hopefully smaller, single-button battery holders to try. Adafruit has one that can be sewn into clothing. I'll see how it works and let you know--but then, it also depends on your costume and how easy it would be to hide something on it.