2008 rx 350. had a new alternator installed about 6 months ago along with a new battery. wouldn't start yesterday. jumped it and started. checked alternator with test tool and showed 14 volts as high output. battery showed 13 volts. went to start it later that day and wouldn't start, charged the battery for 3 hours and charger showed full. started up. went to start it this morning and it showed no charging on alternator and about 6 volts on the battery. tried it this afternoon and started, showing 14 volts for alternator and 13 for battery. Maybe an electrical issue? i'm not a diagnostic person and wife's on my case. Any help would be greatly appreciated. Car has 301k miles. Thanks in advance