Battery capacity

Anybody else have problems with limited battery capacity!. My bike does has an alarm fitted (although it is not supposed to put too much of a drain on the battery). If I leave the bike for any length of time (say a couple of weeks) and have trouble starting it up, as I recently did during the really cold period, then a couple of days later try and start it up again but this time low and behold not enough power to even turn it over!.
Any body else having trouble with crap battery capacity?.