Do you have access to a 110 outlet near where you park your car? If you do grab yourself something like this. It comes with a quick disconnect so you can quickly unhook it when you do want to drive your car.

If you don't have access to a power outlet, but you do have access to sunshine, the same company also makes this. You can leave the solar panel on the outside of your windshield as long as you don't think anyone will steal it, or you can get creative with the wiring so you can mount it inside the car instead. If you don't have a lot of 12v experience I'd suggesting getting help from someone who does before attempting that though.

Lastly, if your 12V battery is currently dead and has died multiple times, you're going to want to replace it. Every time your battery goes dead it does significant damage to the internals. This will severely reduce the battery's capacity and can leave you stranded, so make sure that your battery is in good health. Before you replace it, you can bring your current battery to any auto parts store and they will test it for free.