I have RX400h SE 6 months old, did not use for three weeks due to hols would not start, flat battery.
Was told by dealer service deparment that this is normal. Find this hard to believe as over 75% of the time ( gestimate ) it runs on petrol surly, a 40K car would have a battery that would last longer than three weeks?
I have no great kowledge of the electrics/mechanics re above just find hard to believe,

Frankley this is normal, i have a tvr that i only use occasionally. I installed a trickle charger in the boot as the battery was always going flat and the battery is in the passenger footwell. Car batteries surprisingly dont hold charge that long really with the constant drain from the car alarm. And you would be surprised how much power it has to put out to crank over the engine. 3 weeks without any input is plenty to flatten it out. If u can get some power out to the car, get yr self a trickle charger for next time. but constant flattening and charging kills yr battery eventually. Im forever buying batteries for my tvr as i use it so little, thinking of disconecting the alarm when its laid up for long periods. Ive had 4 batteries in 10 years and its only done abt 3k a year if that. Id say yr battery went flat after a week and a half, let alone 3 weeks.