I had the same problem. I do 2 things:
1. I bought an AGM battery. Much slower self-discharge rate. Bought from these guys. Good price and free shipping:
Exide EDGE Automotive AGM Battery | Exide EDGE AGM Batteries - Battery Service Corporation
2. I disconnect the + terminal (I also remove the frunk lid catch. Super quick and easy, and no chance of locking myself out of the frunk). That way I can leave the battery with no charger for a month or longer with no worries.
On my 2003 all I have to do when I reconnect the battery is set the clock. Nothing else to reset. I'm not sure about the 2002 (radio code?).