Had the battery go flat tonight thought must have left something on so jump started drove for about 45mins to get home thought that would charge it up. Got home turned off and turned back on again fine. Now about an hour later she wont start, dead battery. Since she could get enough charge in her while driving id say the alternators fine. but should a battery just go like that in the space of an hour. nothing was on and couldnt hear the fans going. Is this as simple as replace the battery or do i have other problems ? 04 reg andasume the battery hasnt been changed so probably due after 6 years.