I agree with Brock ... look for a fairly large issue. Either a drastic battery failure or a load on the battery that remains when the ignition is off. This is where a multi-meter might help to provide answers.
I would probably take the positive lead off the battery. Set my meter to read 10 amps full scale initially and then place the meter leads in the amps connector on the meter. Taking the lead ends, connect red to the battery +ve lug and black to the wire that used to connect to the +ve terminal. Do you read any current?
If very low now go to a ma scale and read the current draw. The only current should be the clock, (I think) Please correct me guys if not quite correct. If its a fairly large ma reading then someting is draining the battery and needs to be identified. Obviously remove the load if identified.
If no extra load then I would suspect the battery itself. You might need to take it to a battery shop that can test it under a substantial load using a purpose built meter.
I purchased a Ctek MXS 7 and then fitted the remote charging point that I cable tied in place so that I can easily connect the charger at any time without removing any plastic. I like the pannel mount but did not have time to cut a hole in the plastic to do a neat job. Also it did not come with my kit as did the other item. So I kept it simple. I am very happy with it as a charger though. I beleive the Victorian Police use a lot of them on their vehicles.
http://www.ctek.com/au/en/chargers/MXS%207.0