Dead Battery

[72Chey]

I've had my 72 K20 for 6 months now with no issues. On Monday I go out and turn the key and nothing. I had a Dr. appointment so I didn't think much of it. Just rolled it down the hill and popped the clutch. (Thank God for 4 speeds!) Left the Dr. drove around all day with start ups and of shut offs. Tuesday morning, dead again. I thought the battery wasn't holding a charge (it had no numbers on it and just said ValueCraft?) so I put a new in and it fired right up. Today, dead. So it's not the battery. Maybe a draw someplace? Alternator? Fuse? I don't know if this matters but we recently got our first rain (A heavy soak too) and the first time using the wipers. Maybe irony. Any theories? Thanks fellas