Dead battery and oil life question

[mountainbiker]

My 06 H3 doesn't get much use due to my schedule. I bought it in Aug 06 and haven't even broke 3000 miles on it. The battery issue isn't helping. The original AC Delco had to be chucked as soon as I get it to Germany as it wouldn't even take a charge. I couldn't get an AC Delco replacement, so I went with the Optima Red Top. Unfortunately, it won't hold a charge beyond about 10-14 days. If I drive the H3 about once a week, it seems to keep enough juice; unfortunately, I don't have the luxury of driving it once a week.

The H3 is sitting next to a 97 Explorer. It goes weeks and weeks at a time with out running. I was recently away for 6 weeks, and it still started like a champ.

Therefore, I am scratching my head. Can the H3 actually have 2 bad batteries: AC Delco and Optima? Or, is there some sort of parasitic drain (no PIAAs, no new stereo, no alarm ...)?