i had a issue with this couple months ago where my battery wasnt charging so i replaced the alternator and my battery was charging fine after that.
now since 2 weeks ago my battery has been going dead while the engine is running!
i checked the cables, fine. the light in the dash goes out and stays out once the engine is on (it is also completely out and not DIM)
heres the very annoying part of it the battery takes charge from a jump start and from a 240v battery charger! but not from the alternator!!
its driving me completely insane and cut my holiday short because i didnt want to be stranded!
could someone please give me a hand on how to properly troubleshoot this problem because no way in hell i can throw around cash to buy new battery and alternator here and there!
Replace the shagged battery with either a new one or a known good and recheck the Alternator charge voltage 12.77 is too low as is 12.6 at idle but as stated previously the Alternator regulator can be tricked by dodgy batteries. You can't have dropped one phase of the Alt as it is a new one unless you are deadset unlucky and got a dodgy new Alt
You will never sort out what is wrong with the shagged battery in circuit... well, not 'never' but it will be much more difficult.
Once the battery is sorted look for dirty/corroded/frayed connections on the battery and earth cabling and to help fault finding... take a reading withe the Positive multimeter lead on the Battery + ve and...
1 the -ve lead on the -ve battery terminal
2 the -ve lead on a good chassis earth
3 the -ve lead on a good engine earth
4 the + ve lead on teh Alternator output and the - ve lead on the engine earth