Leaving in parking lot for 15 days - best way to save battery

[1995E]

I for one am really concerned about the batteries and/or the drain on them by the Explorer. I have already had one replaced a few months ago and the other day when I was looking through some features in the Explorer with the push button in the 'ON' position (vehicle not running) The radio shut off and the message Battery Saver Program OFF came up. This is the same thing that happened with the previous battery. Perhaps it is because I don't drive it enough (just over 9000 miles in 2 1/2 years) to fully recharge the battery after it sits 2 or 3 days. I think the electronic systems that require a small but constant amount of power to stay functional when the vehicle is turned off place a greater demand on the battery than that is found in most vehicles.
There are other posts about having to replace the battery, some just after having had the Explorer just a week or so.

Peter

Wait, don't the batteries last for 10 years? How could not recharging them for a bit kill the battery?