alternator-Battery question

[G-356123]

When first cranked, alternator/battery gauge show +14. Roughly five minutes of running, gauge shows discharge (maybe 1/4" on negative side). Multimeter of battery shows 12.3-6, when not cranked.
Alternator (when running) shows 14.4 on initial start), then drops to 13,6-8 after a few minutes. Is the alter or battery bad or both.
Any help would be appreciated. This is all I know how to check.
Thanks

 

[zora]

see you other identical post

Alternator-Battery question

2007 Silverado 4.8L When starting engine, charging gauge reads past 14 or the positive side. After driving for approximately 5 minutes, it will read less than 14 or on the negative side. With a multimeter, the batter reads 12.6, with engine off. Alternator will read 14.3 when engine is first...

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