Congratulations,
That's your personally delivered entry pass to the 'is it the alternator? Is it a parasitic load? Is it the starter motor? Or is the battery just halal?' game.
Once you hear click click click click its usually the battery is halal, sometimes you might be lucky enough to get the very slow half a turn over of the motor, then the clicking.
As per the others - charge up battery on the battery charger, then load test with a carbon pile load tester - your local auto electrician will have one of those and usually battery tests are free
While they're there they'll usually do an alternator test, multimeter set to 20V, all your lights and electrical accessories on + fan up high and AC then check the voltage across the battery terminals at idle 13.
4V-14.8V - A-OK.
Then do it at 2000 RPM as well.
Then make sure you buy one from them if its just the battery thats halal, rather than the flogs at Burson/Repco/Autobarn/SCA - they'll likely be more competitive on price.
If the battery is on the old side usually the draining it dead flat trick is the death blow to them.