batteries

my doorbell died. it's a remote wireless type thingy. anyhoo, it's got batteries in both parts. the ringing bit and the bit on the door. i changed the batteries in the ringing bit. still doesn't work. ok, i couldn't get the bit from the door opened to get the battery out so i took it to work for B to try for me. he's so helpful. :) i bought the batteries tonight, yes, batteries. i only need one but they are in packs of two. then i remembered buying the last one. it was in a pack of two too. it's around the house somewhere. they are not cheap. of course i can't find it now can i? that was ages ago and it probably wouldn't work now anyway. my question is: why do they sell them in packs of two? do other things that take these batteries use two? i doubt it. it's not your normal common everyday battery. it's special, read expensive. it's the same with most things these days. i bought some screws recently for the kitchen shelf and i needed eight. they only came in packs of six. does the phrase gotcha by the short and curlies ring a (door) bell?