Disco 3 (LR3) Battery Drain

Hi Just back from Devon this afternoon and found my LR3 battery to be completely flat. Had a couple of issues with slow starting the beginning of last week so changed the battery for a high power item. This is the 1st time the car has been left without using it every day so suspect a heavy battery drain. Am used to chasing battery drains on L322 Range Rover but not LR3. Also found the suspension to be completely deflated and on the bump stops, I know I have a leak somewhere as it is usually a bit low on the back most mornings. Could the car be continually trying to repressurise the system?
Put the old battery back on which had been charged and the car fired up fine and jumped back up to level in a few seconds.
Any Ideas?
Cheers Ian

First of all check the charging system which means at least measure the voltage on the battery with engine running... most common cause of voltage drop on these vehicles are the alternators which can cause quiescent stationary draw even if they charge but are not in 100% perfect condition. The best is to check it with oscilloscope cos it has a 8 p/n junction rectifier pack and if only one of them is failed it will charge with good voltage but there will be a drain through the shot diode https://www.brighthubengineering.co...w-to-test-an-alternator-with-an-oscilloscope/