Hi,
I have had had problems with my own vehicle relating to the charging circuit and diagnosis has certainly taught me a few things!!
If you open the bonnet (assuming a fully charged battery) and test with a multi meter on the battery terminals you would expect around 12 volts.
If you then turn on the ignition you would see a very small change in this reading.
Then turn the key and start the engine and read the meter again and it should increase to between 13.8 and 14.8 at tick over.
This proves the alternator is functioning.
If you have no battery light on the dash check the D+ wire from your loom to the alternator. Normally black and only one with a thick cable which is the positive to the starter.
I agree with some of the other comments on the drain which is a lot harder to trace.
Cheers
Mark
