I have a 2005 Chevy silverado on my way home from work my battery started draining and did so until drained. All gauges n lights quit as well as truck. what's my issue

Has to be the alternator, one way to check is yo start it then unhook the battery and if it dies then it's your alternator

Do not remove battery terminal while vehicle is running this can destroy the computer. You could do that with the older vehicles to check if alternator is working but not with the newer vehicles with computers.

Have alternator tested with a volt meter with vehicle running should be charging at 14 volts. Is the battery light on ?

remove the battery to service it, charge it up. the charging system did not work so the rig ate the battery. with a charged battery, you can begin diag, you could also just remove the alternator and take it to be checked at the parts store. they could charge and kinda test a battery. generally speaking. if it's totally run dead, you need some serious time on the charger, that may be best done by a shop with a substantial, adjustable pro type charger and take over 4 hours, multiply by 3 for a home trickle charger. if you can check the water, add distilled where needed, if its sealed go by the green eye. you can google that and read about how some indications tell you something. charge in a well ventillated area, clean the places where cables attach with wire brush. pop the battery bolts out and use them as charging posts. inspect wires, connections, power distribution center and fuses. see what that info does for you.

Depending how many years that battery was in use, you could save the trouble and time by replacing it with one that has a good rating for time, amps, and warranted several years. it has been deep cycled and run totally ead, that does not bode well, and after a few of those, it can be internally compromised. takes careful handling to save it. not have it explode, and continue to give service.

note any connection trouble, they seem to use less copper every year, the metals are not necessarily what they once were, and plastic is taking the darn thing over, even some of the battery bolts are too short and longer ones could be needed. cables may have issues, distibution box connector, system ground to the frame, body, and engine must be verified, then the warning circuit must prove out, the volt indicator may need to be monitored and compared to a DVOM reading as others suggested. Your amps output can be tested with a shunted ammeter and the control voltage of the regulator must be in spec. there must be no parasitic load over, say 150 mA unless explained in specs or momentary. you need a tech before this is all really checked right, so basics first, then finish with verifying tests. then you can trust it. (A/C delco has the best internal circuitry in their regulators) just sayin, it protects against repeat failures or electrical novice accidents.

It is likely the alternator or associated wiring. Take a close look at battery cable connections and the alternator connection. What ever you do, do NOT unhook a battery cable while the vehicle is running. Also the reason why the battery is discharging while driving is that the alternator is not charging it and the electronic fuel injectors, ignition system, etc. is taking power from the battery. If the battery is not getting a charge the vehicle will soon quit running do to insufficient power to the electronics.