Have message center problems battery icon stays on,service 4wd,service engine soon

What is your question?

My 2001 Duramax Deisel 4x4 Crew Cab in the message center my battery icon came on the day after i towed a rented horse trailer and volts read 10 to 12 amps but my battery icon stays on in the message center. I have an appointment on Monday for a diagnostics is the way to go please help? Plus Service 4WD message comes all so Service Engine Soon I have 174,400 miles I need help bad?