Thanks for the reply Zardos.
To answer your question re the wiring of x-charge to alternator. The reason behind this was purely due to following the official x-charge fitting instructions.. http://foundry4x4.co.uk/pdf/X%20Eng%20at%20Foundry%204x4%20X-Charge%20Instructions.pdf
In response to your other points, my vehicle is a big gas guzzling v8 so unlikely to be venturing too far. The only thing I can foresee me running without the engine running might be a fridge one day.
Most of the extra equipment it will have will be needed while engine running. For example winch, compressor, air-lockers, and extra lights.