This might help you
This might help ,Battery Drain, Mysterious or Unexplained
I have had a number of owners write in complaining of unexplained battery drain. For example, Jeffrey Eyestone has had a strange problem with his 1996 Range Rover 4.0 SE since he moved to a condo with underground parking along with 150 other vehicles. It acts as if his Rover’s computer senses other keyless entry systems and it “activates” at a higher level, draining battery power – to the point that his brand new battery can be drained in about 4 days of inactivity. The dealer replaced the battery and tested for excess drain but did not find anything. Jeffrey reports: The problem persisted and now they tell me things like “Oh yeah, when people leave their Rovers at the airport for a week at a time, they have this same problem. Perhaps you should consider installing a battery shut-off switch under the hood.” More recently, Frederick Jauch reported a problem that has been going on with his 96 Range Rover over the past 5 months. His battery drains within 2 days of not being started. The dealer has replaced the battery, battery cables and alternator, at quite an expense to me, yet the problem persists. The mechanics claim that it is shutting down properly and can find nothing wrong with it, but have suggested hooking it up to a charger nightly (not going to happen).
The usual cause of these difficulties is problems with the remote locking system. In December 1996 a Technical Service Bulletin was issued acknowledging the remote handset was subject to being activated by static electricity. A new replacement part for the remote handset, STC3637 was announced. The system was still subject to interference from power lines and other vehicles' remotes powering up the BeCM periodically, so another modification was introduced in November 2002 (UK vehicles) after production of the 4.0/4.6 had long since ceased, a new RF receiver (part number YWY500010). No such official fix appears to be available fo US vehicles (which use a different frequency) -- if you hear of one please email me. Meanwhile Jeffrey Upton came up with his own solution (he lives near Logan Airport in Boston and suffered this problem frequently). He disconnected the leads between the window RF antenna and the receiver. In this condition the remote still workls fine as lopng as you are within a couple of feet of the vehicle, but the effect of external radio interference is eliminated! In general, try to park your RR away from large parking garages where people are coming and going in other vehicles whose remotes may wake up your BeCM too often!! (See the Alarm/Security System page for more details).
Of course it is equally possible that mysterious battery drain can be due to other causes that might occur on any vehicle. Staffan Tjernstrom reported that he has twice had the experience of coming out to the garage and a dead battery. In his case a dead cell in the battery was diagnosed after a very interesting drive to the dealer with just about every single control / light in the car set to 'Lucas Random Activation Mode'). The dead cell would sometimes cause just enough of a drain / back-voltage to look like a drained battery. Plenty of other possible causes exist -- common ones include the door outstations and locks, bonnet (hood) switch, and faulty heated windshield relays. To track own the cause, just follow the same procedure you would on any vehicle --ie put an ammeter in series with the battery and read the current while you start pulling out fuses til you notice a change. Even in the best of circumstances you will probably not be able to get the drain below about 50-100 mA, due to the draw of such things as the clock, radio memory, alarm system and periodic EAS operation etc. However this amount of drain should take at least 2 or 3 weeks to flatten the battery. If you are still unsure as to how to proceed, Andy Cunningham has an exhaustive description of how to trace down battery drain at this link.
Yet another possible cause of battery drain is not putting the transmission in Park. Ron Beckett reminds us that the shop manual contains this warning: "WARNING: Always leave the vehicle with the gear selector in 'P' (Park) position when parked, even when the starter key is not removed. Failure to do so will result in the battery discharging.
