Think you have answered your own question there.
I am only used to Disco 1s and 2s and they are not such a problem when you disconnect and reconnect a battery. Progress I suppose!
So now I would be into the field of suggesting you have a second batt connected in parallel at all times to give you twice the power available. Have the second batt connected up but have a cutoff switch in the positive lead so that you can disconnect it/reconnect it whenever you want it. Then you wouldn't lose your alarm codes etc, but would have the power when you need it for starting etc.
Feel your pain mate. Modern car electrics are a complete nightmare.