Dead battery

[McLoffs]

I came out to my 1993 300E today after work (it had sat for about eight hours) and the battery was dead. Completely dead. As in, the car wouldn't turn over, the dome light would barely come on, etc. I was able to get it jumped and get home, and am thinking I might need a new battery.

However, I'm curious about how the battery could completely drain after sitting for that amount of time. I checked various lights, accessories, etc., to see if anything was on/draining power, and found nothing. This also happened once before, but the car had been sitting for a week and I figured it was just because of the time.

Anything particular I should be looking for?

Thanks,
Mike