A healthy battery, regularly enough used i would imagine would be of no issues but i think that it is the irregular usage which makes a three year old battery age (they do recommend changing your standard battery every three years anyway).
I do not understand the world of electrics, car battery or otherwise and am not aware of how any electrical shielding (if any is required or used) would degrade over time and would adversly effect battery usage. To my logic (and it is not a conventional one...me being both thick and! weird) the only problem and old vx has to offer (battery wise) is the old battery sitting so snuggly in its 'jaws of death'..(..try removing one with no injuries and you're a better man than i lol ).
Age and it's related electrical issues on any car (and i'm happy to be corrected by those that actually know what they're talking about) can mainly be traced to componant fatigue and weather/dirt ingress and any handbuilt car will suffer more in all those areas, as build quality and chasis stiffness will eccentuatate their effect.