Don't you find it annoying losing all the settings in your car? Radio stations, etc.? If you're leaving your car for a long time without driving it, I would suggest adding a pigtail to make it easy to plug in a battery tender instead.
Not really. I lose the presets, but I play music from a USB stick anyway. It's far, far less trouble than coming back from a trip and finding your car dead in the airport parking lot. Many times I've also discovered a dead battery in the morning because the door wasn't closed all the way and the interior light was on. Ugh.
Having a separate "tender battery" for car-is-off power needs is a fine idea. Another idea is for a battery voltage monitor that will cut off the battery if the voltage starts to drop.
They're not cheap, but Antigravity batteries (1) implement that. It monitors battery voltage and disconnects when it reaches a given level. To start the car you just press a button on a fob to internally connect to the reserve, and off you go. Doubly useful for Lithium batteries since they really don't like being over-discharged.
