A Battery Tender or C-Tech battery tender will be a good investment if you plan on frequently storing the car. They will pay for themselves quickly in terms of not needing to replace batteries and for convenience. The C-tech can even bring a sulfated battery back from the dead in some cases.
A fully charged battery will live a lot longer than one that is charged and allowed to run flat.
Don't use a cheapo trickle charger for an extended time as it may catch fire, explode your battery or at least over-charge the battery and kill it.