Measure the battery voltage 10 mins after you get home after a drive, then a few days later brfore you go to drive it, battery voltage should be almost the same, if not try it again with all the fuses pulled out and see if the problem disappears, sound like something is draining the battery, and you may also need your starter reco'd. as when the brushes wear, they draw heaps more current on startup, if its got over 150,000, its probably due to have the starter/alternator freashened anyway, as they are over 10 yrs old now.