How long should a RRS keep it height if it is not used ?
I would think at some point the air system would stop topping its self up to save on battery life.
I have read the manual but it says nothing about this.
I work away for home quite a lot and the RRS will be sat in the garage for two - three weeks at a time.
Any info on this would be great.

It doesn't top itself up at all. What it does is wake up periodically and, if it finds it's not level, it levels itself downwards by releasing air from the system. You can avoid this by parking in access height. Make sure you select access height before you stop; this reduces stress on bushes and tyres. If you put it in access height with just the handbrake applied and whilst stood outside, you will see the front wheels rotate slightly as it lowers. Doing this with gearbox in park will obviously load things up in the gearbox and suspension. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

What you're seeing could be because of a leak or bad suspension calibration but it's normally just uneven/non-level ground.

If you want to check for a leak, remove Fuse 26 in the Battery Junction Box and see if it still drops.  Visiting from DISCO3.CO.UK
2006 Discovery 3 TDV6 Auto HSE Zambezi Silver

The strange thing with my one is that it stays at height for just over 2 days then the back starts to drop.
I have tried removing fuse 26 and the same thing happened.
Thanks for the info RRSTDV8 that does explain a lot, so it does not use any extra battery power, that is good the know.
If I drop it to park in access mod would this just hide the problem or will it still drop from there.

When I got it I was given 6 months warenty so do you think I should take it back and have it checked.
It is not causing me a problem just now as when I start it up the suspension works fine but I do not want it to get any worse.

If it need fixed or looked at I would like to get it done now and hope it saves me paying for it later.