Very late reply and possibly not relevant but an often overlooked "battery problem" is a tracker unit fitted years ago by a previous owner. The batteries on the average tracker doesn't last more than a few years in real world conditions and once it's lost the ability to hold a charge it creates a high drain condition on the vehicle battery. Worth checking out. Can be difficult to locate since the units are intentionally hidden away. Not sure this helps you but may help others down the line. A good first step would be to verify whether or not a tracker unit is fitted in the vehicle (national database perhaps?)