I came to my car the other morning to find it almost completely dead.

At first I figured I must have left something on, but there was no evidence of it. One thing I had done the day before though was a long drive.

The car has been doing shorter drives of say 60km total a day fine for a week now since I jump started it that morning. But the voltage sits at a consistent 13 volts for the trip, except for the beginning where its usually at around 13.5. Engine off its around 11.8.

Initially I suspected the battery but its only 6 months old so im really unsure on this one.

should sit on 14 volts i think might be alt.

yeh sounds like a dying alt.
most battery places will test your battery (and alts charging) for free.

Sometimes the alternator may charge ok but if a diode is failing it allows the battery to slowly discharge.
As suggested, get it checked, try asking an autolec if the do free quotes. I always suspect battery places of only finding the results they want ie sell you a battery and they may not be able to test the diodes. Before doing that, check your electrolyte levels and use a mains charger to fully charge the battery overnight. If it still fails to work in the morning, it's probably stuffed.
You fellas are probably right about the alt. but those figures could also be caused by dirty battery post connections.
Cheers
Paul

one thing i remember being told about car batteries is once they go flat they are f**k and will never work the same again.

if its gone flat with no apparent reason then replace it with at least a 550CA one.

i always suggest getting the biggest battery you are comfortable fitting in the car and paying for...

could be the alternator, but if the voltage drops to 11.8 with nothing on, the battery aint looking too healthy, a charged battery should sit at 12.5 with no load on it, charge it overnight and leave it disconnected from the car, test it again a couple of hours after taking the charger off (to let it settle as it will read higher than 12.5 after its been charging)

voltages depend on a few things, where you are physically checking them, how accurate the meter is that you are using and what the electrical system is doing at the time, ie after start up the battery will need a slightly higher charge to recover from starting the car, so voltage should sit a little higher, same if there are other loads on the system, aircon, thermo fans, etc etc.

from my experience, a charged battery with no load should sit at 12.5 volts, anything less check the electrolyte and give it a good charge. 10.5 is considered flat for most car batteries.

car running and alternator charging anywhere from 13-14 volts, depending on factors as stated above... typically 13.8 though for me...

hope you sus it soon and doesnt cost too much!