hello do i have to go to my dealer for synchronizing of my becm and ecu every time my battey goes flat or is disconnect
costing me a arm and leg

Greetings my friend, first of all it would help if we all knew what variant you have & year as from what I read & hear this can make a whole lot of difference.
If it a 2.5 diesel then on my experiance of my 1998 2.5 DSE I can give a little advice.
First of all you need to establish what is causing your battery to discharge. going on my experiance and many others the fault will probably be with the alarm RF receiver in the rear of the vehicle. If you don't have the modified version then the original factory fit one is prone to interferance from all sorts of stray signals, IE other car remote alarms, mobile phones & wirless networks. These will all trigger the BECM to wake up and cause battery drain. With regards to having to go to a mainstealer each time to get your key fob to re-sync this should not always be the case depending on the year of your P38. I believe that post 1997 modela do have the ability to re-sync via the remote fob (If this is not correct anybody please advise) when I had this problem of the engine disabled warning on the display it should also read press remote & on doing so should re-sync your key fob. Also do you have the EKA code to try via the drivers door lock. another solution is to invest in a black box solutions syncmate. I'm sure you will get further advice on here as thera many of good people here to help you like they have helped me.
One last thing I forgot to mention. a quick way to tell if your BECM is having its regular sleep is to check for the red light inside the car on the H gate transmission next to the letter P. Switch of the engine remove key from ignition and ensure all doors / windows are closed and all lights are off & radio. watch this red light it should extinguish within about 5 minutes, if it does your BECM is having its nightly nap, if it does not this could be your battery drain problem.

is this the same DSE you had probs with not so long ago? with the sujested RF unit being at fault?

Worth remembering that there are two different sync problems that P38's are prone to. Mark has mentioned both in his post but it worth emphasizing that other than being caused by flat batteries they are not related. You mention in your original post that you are referring to the sync between the BECM and the ECU. If this is the problem you can buy a Syncmate from Black Box Solutions or one of their UK resellers for about £100. Well worth the money but make sure you buy the correct one for your engine (Derv, GEMS or Bosch).
So now that you can resolve the problem when it happens you can focus on finding the cause of your flat batteries. Again I'm with Mark on this and suggest that you check the RF receiver .

As above but consider a Nanocom EVO rather than a Syncmate as you will not only be able to re-sync but read and clear faults on all P38 systems.

thanks for the info its a 2,5 dse 1998 r reg.i have replaced the rf receiver with a brand new one from land rover
they told me it would be £209.00 pound i said you are selling them one ebay for £164.00 he then said oh ar mm eerrr yes we can sell it for that.when i left i said if i bought one for for £209.00 would have refunded the difference of £45.00 pounds he told me who would need to speak to the manger.
robbing bastards duckworth land rover kirton.
well i hope i have sorted out the flat battery problems just need to get it started now after a dead flat battery
any more help would be great

Ok EKA code has nothing to do with ECM BECM security code. EKA code is used to unlock alarm system. When fob is pressed it sends a signal thru RF reciever to BECM, if key code sent is same as code stored in BECM car unlocks and alarm is turned off. If BECM does not recognise that code or it has been lost, because BECMs get a version of Alzheimer's when voltage is lost. You will get engine disabled message on centre. Engine will NOT turn over with this message present. When you feed in correct EKA code or on some vehicles press key fob with battery fully charged that message should go away. If that message is not present and engine turns over but does not start. You will have lost security code sync ECM to BECM. That MUST be reset with diagnostics it CANNOT be set any other way. When the ignition is turned on BECM compares a code stored in it with a code locked in ECM. Those two codes MUST be the same or car will not start. If BECM has had voltage removed it forgets this code and quite often inserts it's own weird and wonderful set of numbers. A Syncmate deletes these, reads the code locked in the ECM, and writes it into the BECM. Then the engine will start. If you have lost that sync you need someone with a Syncmate or Nanocom to reset it for you.

Sync mate sounds like what i need to get
thanks will let you know how i get on
another 100+ quid

hi rdsc , p.m. me and il'l give you my no may be able to sync it over the phone ,,cheers mozz