Hi all, as the title suggests, my battery light on the dash has recently come on, then one day the vehicle wouldn't start. I got my charger pack on it and it started fine I gave it a good long run yet the light stayed on but the car started first time no problems until this morning, when it was dead. Jump started it to get home, turned off and then it wouldn't start again. I put a multimeter on the battery and it was dropping slowly as I was watching, nothing switched on in the car and not running.

completely lost as to whether it's just needing a new battery or does it sound like some thing else is playing up? why is the battery voltage dropping like that?

Sounds like the alternator to me - probably a diode failing - so draining the battery - can you smell any burning ?

Without the diode, the alternator becomes a motor and will drain the battery - but will likely smell of burning as it won't be able to turn as it wants to.

I've not smelt any burning, would the alternator still kill the battery if if the engine wasn't running?

I would suggest you need a new battery, Td6 alternators don't appear to cause problems.
To be sure charge the battery up and then disconnect both the terminal cables and measure the voltage, preferably over a few hours if you can.

How old is the battery ?

the battery is only 2.5-3 years old I reckon. I'll try disconnecting it and as you say measure it over a few hours. cheers

If you have another vehicle - take it to Halfords or Euro Car Parts & they will test it for you

Have you measured the alternator output with your multimeter.

Not entirely sure how id do that? I took the battery off and charged it over night and part of the day, once I had disconnected it, it measured at 12.02v then I left it till the evening, off charge still, and it had dropped to 11.85v having not been used. I placed it back on the car and it started but as soon as I had switched the engine off it wouldnt start again. i measured the battery on the car and it had dropped to 10.23v........

You need a new battery, is it under warranty by any chance

well that's some relief I guess, instead of forking out for an alternator, I'll look at a battery. I looked through all my paperwork but I can't see anything so can't prove anything for warranty plus the guy i bought the car off said he had put it on new then. 🤥

cheers everyone for the advice and replies.

When you get your new battery fitted you can check the output voltage of your alternator by simply measuring the voltage across the battery terminals with the engine running at about 2500rpm. You should get about 13.9 to 14.2V depending upon what you have switched on in the car.

That's brilliant thank you. I'll try and get a battery tomorrow and give that a whirl.

well I've just fitted the new battery (12.53v) and it's starting each time but the multimeter is still saying 11.7v when the engine is running and the battery light still comes on. My iid tool is confirming the voltage too.

its now steadying between 11.9 and 12v

EDIT: iid tool is showing green 12.2v now. maybe it was just taking it's time.