Due to not using my car during this lat few weeks, the six (+12v) battery went flat. This meant I was not even able to open the car. You need to use the emergency lock to open, then open the boot and put the battery to charge. I did this until the battery had enough juice to open the car as normal. Then I left the car charging over night, on the assumption that the main battery will charge the aux battery. For a couple of days this looked true, however I left the car in the garage for about a week and the problem re-ocurred. Is there any proper way of charging the 12v battery? . How do you maintain it if you are not using your car? On an ICE, all you need to do is start the car every so often to charg it. How does the aux battery get charge normally?