losing volts....why?

about 2 days ago i started the truck and the battery guage was down to 11.5 volts. i took a 45 minute trip and it dropped down to almost 9 volts. is my alternator not charging or could it be a grounding problem? its a daily driver.

the altenator could be going bad but isnt completely dead yet or it could very well be a ground man.. id get the alt checked and take it from there, it might even be a cell in the battery going bad..

put a multimeter on the battery while truck is not running should be around 12 to 13 volts, if not the battery is bad
start the truck , now while running put the multimeter on the battery, it should read about 14 to almost 14.5 volts, if it is still reading under 14 volts it is a bad alternator, and always upgrade your grounds to a min. of 4ga straight to the frame, and one 4ga to the block of the motor, to receive the best charge