Battery/alternator question

2002 520

110k on the clock

about 10 weeks ago, it started needing a jump in the morning, got a guy to look at it and he said battery, relatively inexpensive so I put a new shiny battery in.  yaay I thought.  about 3 weeks ago, it started needing a jump again.  boo says me. 

Dropped it into local garage who's been doing my services for me and Id trust, says its actually alternator,  new one costs circa 750e, reconditioned one was 360e.  (does this price sound right for a conditioned one)  anyway, I went with the reconditioned one on the recomendation of garage who said it could be done.  got another 2 weeks out of it, but battery dead again this morning. 

I gotta drop it back to garage but anyone any suggestions if its not battery and not alternator?

also, its absolutely chewing the oil.  I gotta do a top up of 3-4 litres like every 8-10 weeks.   no leaks on the driveway.   Is that just part of living with a car that old?   I tried one of those viscous additives (dont ask me the name) on the last topup thats supposed to elongate the life of the oil but it didnt. 
 

andrew, thats for taking the time to respond.  very helpful answers.  Yes, its the e39.  

On the alternator  its a bit "holy jaysus, how much?" but if thats what it is then it has to be.  I rang a bm garage yesterday and they confirmed not much change of 750 for a new one so half that sounds right for a recond. one.

Yeah, the drain on the battery is a funny one, the only thing I can think is there's an electrical short somewhere.  It took a bang to the back passenger side about 2 years ago, I got what I thought was properly repaired but after I got it back shortly afterwards the boot loaded cd player stopped working.   My garage said theres a break in the electrics there and it would be pricey to start opening up things to see where the break was and as I dont really listen to cd's that much I never got it fixed.  Possible theres something there.

WRT the oil consumpsion, do you get any white deposit under the oil filler cap? Also if you take the filler cap off when the engine is running does it start to idle roughly?

If the answer is yes and no to these questions then your CCV is knackered. It's not an expensive part to buy but fitting it is a pain.

Crispy-d wrote: If there is a flow of current when the engine's off then you can start taking out fuses to see when it stops (or at least decreases as the alarm etc. will take a small portion as a matter of course).

I had the exact same problem with mine, after a lot or trial and error and some hair pulling I disconnected the radio aerial, worked a treat!

Alternators on these beasts are not cheap. I'd agree that it sounds like you have a short somewhere though in my experience you could find it quite easily or spend ages chasing your tail. Thing is, if you want your car sorted you may have to bite the bullet.