sylinoid (sp?) bottle

well my 400ex is havin some eletrical problems. im almost positive the sylinoid bottle has gone bad or something, if that is possible. by sylinoid bottle im talkin about that lil cylinder thing by the battery. is there a proper name for this? used to i would just wiggle around on the wires connected to the bottle and tap on it a few times and it would start. well it wont start at all now. i just got done cleaning the bottle with a tooth brush and getin all the ceroded(sp?) crap off of it. still nothing... does anyone know of a way to fix this or will i have to just replace it? anyone know how much they cost?

THANKS