I too have sufferred the dead battery after an extended period of parking,
Lexus replaced the battery stating the old one had ' dead cells' however after reading all the tales on this form and given that I do leave the car in the garage for extended periods I made up a timed trickle charger using an old timer from the gas central heating, a 12v relay and a trickle charger from Halfords
The charger is switched on for an hour each day I am away and since it is connected via a relay it completely disconnects itself after an hour ( that way there is no risk of the battery discharging through the charger)
I fitted a rubber mounted two pin socket across the battery and mounted it adjacent to the radiator at the front of the car
I have used it several times and have had no problems starting even after the car has been left for 30 days