Do you park somewhere that you can use a plug-in battery maintainer? These don't take much power but will keep the battery topped off and ready to go when you need to drive the car somewhere.
The starter draws quite a lot of current to start the engine so if you were to start the car to keep the battery charged, you'd probably need to drive it for 5 or 10 minutes, preferably at a time that headlights are not required and with minimal stop and go traffic (to reduce brake light use and idle speed).
-Rod