Well... as for storing a battery, a fully charged battery can sit on a shelf(or for that matter a bare concrete floor) for about 5-6 months before self discharging enough to not start a vehicle(roughly 12.0-12.4 volts). At 12.4 volts a battery is considered over half discharged(though it doesnt sound right, half of 12 is 6, but in this case, at 12.4 the battery can barely produce enough ampres to sufficiently turn over a motor). Best bet to store a battery is to fully charge it, then depending on the tempurature at which you store it, the cooler the better, recharge it every other month, or as a few others suggest, use a tender. But be warned, even a tender can boil a battery(boil the water out of the battery fluid solution, which is 65%water,35% sulfuric acid). so, with that in mind, you can hook up a tender and forget about it for week or so, unlike a "normal" type charger. We rotate our stock(I work for Interstate Batteries) every 4-5 months. Also, concrete floors will not really harm a battery's capacity, kinda an old wive's tale. The only conclusive testing i've read within the confines of the Interstate Batteries Systems testing is that concrete can infact make a battery take more time to charge while charging it because of the temperature differential, when charging the battery tends to get warm, the concrete cold, and it kinda acts like a heat sink, slowing down the charging process just a bit, and i do mean just a itty bit... do belive that the concrete issue all started way early with lead acid batteries that were made with hard rubber cases, not the plastic cases of today.
One other thing, knowing most of our cars use side-post batteries, please, go down to the parts store and get a pair of side post adapters, the are made of lead, and will improve charging the side post battery much better than using bolts..
hth...