Service Battery Charging System Error - HELP!!

[DuckyDee]

2010 GMC Sierra 1500 SLE 5.3l - "Service Battery Charging System Error"  We have replaced the battery, had the alternator checked, cleaned all terminals and cables including the ground to firewall and we STILL get the error.  Charged the battery up to go 5 miles to the parts store to find out what code is error causing only to have battery completely drain and the truck died.  

 

Owner of truck had a stroke about 6 months ago and he thinks that he replaced the 175 amp mega fuse with something smaller - like 100 or less.  Could this cause the issue?  I'm going to replace it anyhow, but I'm hoping someone can help me figure what is causing the error!

[Brian715]

If you couldn't make it 5 miles without the battery dying, then your alternator is not charging no matter what some AutoZone test tells you. 

[davester]

You'll need to do some diagnosis, as the power output of the alternator is controlled by the ecm.