Thanks for the great advice.
Is it true that the camera will lock up when battery is exhausted and can only be reset with a trip to the service centre?
No. That's never been my experience at all.
The worst case was with earlier versions of the firmware where the camera may start locking up as the battery gets low and the MFDB and body seem to start mis-communicating properly. You will probably learn to know the dreaded 'thunk' sound when the shutter is released as it is different to that of a normal shutter release. It would happen particularly if you had mirror up or auto-MUP enabled and used the shutter timer or cable release to fire a shot.
The worst case scenario would be that you might need to eject and replace the batteries in the body and/or power down and remove the MFDB and remount it. However, it never ever locked up to the degree that you mentioned.
Upgrade to the latest DF and MFDB firmware versions. This is important.
Get yourself the best batteries you can (Enloops for example) or better yet either the new Phase One battery or the EJII battery. Since I've had my EJII battery I've seldom had to charge it at all in 12 months plus my lock up problems have essentially stopped happening. I bought a kit with two batteries but to be honest I could have saved money and just got one because these things are like the energizer bunny and just don't die for months.
The EJII battery was probably the best investment in my DF camera I've made, if only because it saved me from throwing it off a cliff at some point.