[a1supersport]

Are you sure the battery and alternator were replaced? (do they look new?) If you have a voltmeter, check to see how many volts are in the battery. Make sure the battery terminals are disconnected when you check it. Now connect the terminals and check it again. It should read the same...about 12 volts. If it drops down, something may be drawing power from the battery even when it's not running. If everything's ok, start the car and check the voltage reading on the battery while it's running. It should read around 14 volts, more or less. If it does, then your alternator is charging. If all of the above checks out ok, disconnect the battery terminals and have someone do a "load test" on the battery. Any competent shop should be able to do this for you. This will tell you if you have a bad cell in the battery...even if it's new.