Sorry that i have to contradict you again but that information is completely WRONG. Any used BCU is completely reprogrammable with dedicated tester, the only condition is to not be removed from an immobilised vehicle. I've fitted used BCUs not once and they all work, it's a max 10 minute job to program it including the fob's syncronisation.
also if the battery goes flat it's enough to replace it with a new one or charge it to full then unlock with the fob, or if the fob doesnt work it can be remobilised with the EKA code no need to replace any ECU and the instrument cluster has nothing to do with that whatsoever.
I can only go by my personal experience - then share here.
The Land Rover Dealership, who has the best computer called a test book, told me it was absolutely impossible to reprogram a used BCU. They said it had to be a new BCU and wanted 3 thousand something dollars in parts and service (I have the estimate) plus replacement of the door actuator which they said was malfunctioning - and they refused to guarantee the work. Then I took it to an independent mechanic because they told me via email they could do it with auto-logic for $140. When I got there there she started playing games trying to size me up for a new BCU - which she didn't know couldn't be sourced. The dealer said it was a 6 month wait - when they find a supplier. You can call Land Rover Las Vegas and talk to Gary the sales manager. That's what I was told.
Later the indy shop said they could not program the BCU with an autologic.
I solved this problem myself by reading the forums and getting a used same make and model IC, BCU and ECU from Ebay (the indy shop disagreed and showed complete contempt for this solution when I mentioned it) , disconnecting the battery, and installing all 3 at the same time. The car fired up and works perfectly. The door actuator fixed itself (if there was anything wrong with it) and all scans show no codes present.
The total cost was next to nothing.
Not sure what you're talking about regarding the battery. Not only did I replace the battery with a new one - I bought a Oddessy Marine 4 head for $500 direct from Odessy - the most expensive and biggest battery you can get for the DII without replacing the battery tray - it takes up the entire tray and is really bad-ass. This sucker cranks quick and will run solo for 200 hours with a 2 year storage life.
It did not work. The BCU retains the memory of the alarm trip and it would not stop no matter what I tried. When I pulled the horn fuse Rover shut down after 5 minutes of driving.
I can only go by what happened to me. As I said before I allowed the battery to drain and thought nothing of it. When it got below 12 volts ... the alarm went off (continous horn sounding) when the passenger door was opened. Nothing would work. I tried to replace the BCU with a used one and it didn't work . Only replacing all 3 modules at the same time worked. And like i said before - the dealer says they are totally out of stock AND don't have a supplier for the BCU. I called another dealer in and they said the same thing. This time Valeo was mentioned and that Land Rover is looking for a new supplier to manufacture this part and if they cannot find one it will be discontinued.
I hope I helped some readers by sharing my experience.