Flat Battery

[X5NZ]

My 2002 X5 3ltr deisel is suffering from a flat battery problem, I had a new battery fitted in Oct 07 and all seemed well for some months until one day I suffered a flat battery and therefore failure to start motor. I removed the battery and returned it to the auto electric cothat supplied it., They charged it and and assured me it was OK and was showing 885 crank amps. Again all was O.K for a few months then the same thing occured, I then removed battery again and charged it myself until in the green on my hydrometer. Again a few months later the same thing happened again, I jump started the vehicle and took it to the auto electric company, they ran tests and reported that the navigation system was powered up approx 30 mins after the ignition was switched off and drawing 1 amp for that period, once that time elapsed there was no draw. Does anyone know if this is normal.

Regards John X5 NZ