2006 mustang GT - 110k miles - garaged kept 3 owners well kept. Went thorough 2 alternators and a battery, cars electronics started turning off and the car just started sputtering and died, bought a new battery and alternator and the car started at 14.2 volts and will stay there for like 2-5 mins then slowly drops to 13.05 volts sometimes will drop to 12.5 - 12.6 then shoot back up to 13 Volts. Thought maybe I just got a bad Alternator which was NEW not refurbished so I bought a different brand(Duralast) the car was idling and driving at 14.4 - 14.1 for like 10 mins then dropped to 13.6 - 13.5 volts even with everything on. Next day I drive a little longer and notice the car go down to 13.3 - 13 volts, not sure what it is I've checked the grounds even add a ground from the alternator to the battery ground, all the fuses look good non blown. The only thing I haven't checked is the ECM it doesn't smell like burnt plastic and looks clean. The car runs fine just runs low voltage.