Ok - Time for a different angle of attack. Kimmy - you say you only drive the car once a month. Do yourself a favor and go out and buy an AUTOMATIC 10amp - 2 amp dual 12 volt battery charger with auto shutoff when the battery is charged. DO NOT buy one of the cheaper MANUAL battery chargers - if you leave it hooked up you can cook a battery. An Automatic shut off charger can be hooked up to the battery and left on it indefinately and it will keep the battery fully charged and not damage it. Now you will have a fully charged battery even if you only drive the car once every 4 months. BUT - the other benefit to having the automatic charger is that you can use it for this problem. Disconnect the negative lead from the battery and hook up the automatic charger to the battery for 24 hours. If it is still in charge mode (battery is not fully charged) after this length of time - disconnect the charger and let the battery sit with the negative lead disconnected for 12 hours - Then check the voltage on the battery - if the voltage is below 12.56 - the battery is toast - no matter what the dealer says.
Please get the charger - you will be doing yourself and your battery a favor - and try this test - at the least - you will always have a fully charged battery when you let the car sit a long time once we get this problem figured out. - I still lean towards a bad battery.
Morris