
The concrete floor accelerates the problem because it is a heat sink and a
colder lead-acid battery self-discharges at a slightly faster rate. That's
why the old wives' tale of sitting it on a piece of wood on the floor works
to help keep from killing the battery as fast ---- it insulates the battery
thermally. It you'll set the battery down on a piece of styrofoam, it will
self-discharge even slower. The best thing would be to attach a small load
such as a small transistor radio with the volume turned down low and leave it
on constantly, but also trickle-charge it every couple days too to "shallow-
cycle" the charge in the battery. Such mild "exercising" of a lead-acid
battery is the next best thing to completely removing the electrolyte for
storage. If you do remove the electrolyte, may sure you keep separate storage
containers for each cell's electrolyte and put it back into the same cells
when you refill the battery. This isn't so critical for a brand-new battery
in a fully charged state, but will maximize the restored output of an older
battery which may not be fully charged when you remove the electrolyte for   
storage.