[Andy]

I had a 1999 Z/28 for almost 20 years. I bought it in 2001 bone stock with 17k miles on it and never did any electrical system modifications to it. If it sat for extended periods of time it would do the same thing. I put a quick disconnect on the battery and never had issues again after that. I tried several types of batteries, none really made a difference prior to the disconnect. My guess is the security system on the car when locked drew enough power to drain the battery after sitting for a week or two.