A simple solution for you -

Go to "harbor freight tools" (if there is no such store in your area, any tool stores or auto parts stores are ok) and buy a float charger for around $10, connect to your battery and plug into power outlet. No matter how many days you don't drive it, the battery is always maintained and full. Battery likes to be charged all the time, you would have no worry.

Remember it is "float charger" not "trickle charger". Check out this thread:
http://blog.wenxuecity.com/blogview.php?date=200811&postID=25753