Make sure the battery is fully charged before you store the car and then disconnect it. Ideally, you'd want to hook it up to a trickle charger but with no electricity that's going to be hard unless you remove the battery and take it home with you to charge. Before storing your car, make sure that it's topped up with fuel as this will help prevent corrosion in the tank. It's the same for anti-freeze. Lubricate and grease any nipples and make sure the car is clean and polished if you have time. Don't use the handbrake. There are plenty of portable jump start packs that will do the job if the battery goes flat.