my p38 brought this up earlier, dont want to sound silly but is it going to be the alternator or could it be something silly why its not charging. ive put a multimeter on the battery and tis deffo not charging.
could be battery thats deaders, could be leads not connected/corroded. put a jump lead from alternator body/bracket to battery neg terminal and test again. its not a scientific test but it should rule out the connections.
If it's not bad connections, then if the car is high mileage, it could just be the carbon brushes in the alternator. Not too difficult to replace and just a few £'s for the new ones.
defo is the alternator, on way home last nite, hevac unit turned off, came up with gearbox fault and speedo etc went off, eas wouldnt even drop it down the battery was that dead, just got a brand new one from my local motor factors 160 all in