Weak battery - 2007 VW EOS

I don't think it's a battery. The ticking noise along with the dead battery leads me to believe you might have a belt/pulley issue. The serpentine/accessory belt and pulleys are all part of your charging system. It's how your alternator charges your battery. If there's something up with one of the pulleys or the belt (slipping?) in that system then your battery isn't going to charge properly. I have 6 yrs and 225,000m on my original battery in my Jetta - although I have a new alternator because the pulley fell off of mine...

The ticking sounds like the solenoid on the starter motor poling and then due to lack of power in the battery setting back. (common indicator) to check your battery is low switch on your headlights and try to start the engine. the lights will dim or go out if the battery is low.
if they stay bright it is most likely your starter motor or other electrical problem.
so assuming the lights dim your battery is the problem.
ensure you do not have any light in the back staying on when the boot (trunk) is closed. or other electics on such as radio on mute. this will cause a battery to get low while parked.
if your battery is not being charged you will have a red battery non charge light on the dash when your engine is running.
newer batteries have a smalll window on the top which should show green if it is showing any other colour it probably needs changing.
the usual life of a battery is 5 years from new if you have bought the car second hand A previous owner may have put an old battery on the car UMMM. the date of manufacture should be on the battery also if the battery is new check if you have warrenty on it.
cost for replacement in Europe is between 60 and 100 Euro for the US i do not know more any reputable automotive supplier should be able to give you a good deal if not consult your VW dealership.
WARNING batteries can be dangerous if not handled with the correct precautions.they are also heavy and contain toxins.

Hi. The vw do make a ticking noise from low voltage to the relays. The batteries if you have a v6 are 2, 6 volt batteries. Thee are jump start poles in the engine bay, and you use a normal 12v battery charger to charge them at these posts. The batteries are available as aftermarket replacment parts, but are normally no cheaper than the dealership.