The car here is not a Voyager but relates to the fold down DVD player that seems to be installed in some Voyagers.
Car was a Vauxhall Zafira with battery drain after standing for a few days.
All the checks were done on Battery, Alternator, etc, but the only way the car was able to start on its own was to run it every day, or trickle charge it.
One fault found was an improperly crimped battery to chassis earth connection, but it still discharged.
However it got worse to state the new battery went down in 24hrs.
It was decided something was triggering a circuit to reawaken after car went to sleep electrically.
All systems were isolated one at a time to find the fault.
Then it was discovered know to Vauxhall there was a fault relating to the factory fitted Autovision fold down DVD player system.
Fault was software bug in DVD player that caused spontaneous self activation requiring the software to be Re-Flashed.
DVD players or what...

 

Anything with a microprocessor...

Leedsman.

 

1st suspect [of many] is always the radio, see :

Rick's page here. So whilst many things from basic to complex can be the cause, the start point is always the 'always on' culprits, there are :

Always off [after 15 minutes] check last - always live [even after 15 minutes] check first !.

 

Very interesting mate I had a flat batery years ago on a 1976 Ford Escort. Turns out to be thhe boot light switch was on.