If your car is equipped with a car alarm that has a rechargabe battery. The battery is normally recharged via the alternator once the charge rate has got up to 14 amps. If the car is not used for a while the rechargable battery gets topped up via the car battery and this gradually ruins the car battery. The only real cure other than driving the car every day is to have a battery cut off switch fitted.
Another possible cause….
explained as the engine control unit 'waking up' and having a look at the systems periodically, even though the ignition may be off.
One solution is to fix a pair of fused leads direct from the battery terminals to point where they can be connected to a constant monitoring battery charger.
You can place a fly lead in the boot with a polarised socket, on leaving the car in the garage connect this lead to the charger lead and shut the boot. The charger is then reset (most of the monitoring chargers will need a reset on reconnection) and leave the car knowing that the battery is going to be monitored and charged if necessary.
It is important to note that a normal battery charger which cuts out when the battery is charged will not continue to monitor the battery. The charger needs to be a constant monitoring type.
With this method an alarm can still be used, as the car’s electrical systems will remain ‘live’.
Important note. If you do this, don’t forget to put a note in front of the steering wheel to alert you of the charger connection.