Don’t even know what to search on YouTube for this one. Battery dies Monday I go get new battery. My stereo was stuck in eject mode I noticed regardless if the truck was on or off even after opening door which normally kills the radio. It wasn’t surprising that it did not start the following day. Charged the battery and nothing in my cab works. Blew a fuse? Getting my meter out to test battery which again is a brand new optima.

Damn 5V at the batt

No Optima for me I guess...

Your ECU is likely damaged or al least needs a software reflash.
ECU is slang for the computer that runs your entire truck.

I’ve pulled what I believe to be the fuse for stereo (42-RDO 15A). I will charge battery again and go from there.

Edit : @Muricha are you a mechanic or familiar with these gen trucks?

Haven't even read the post...just trying to make heads and tails of your Santa (?) avatar.

Check your grounds, maybe add an additional ground from battery to frame.
Get alternator tested.

My 2009 Sierra is really sensitive to messing with the electrical system.  I have triggered some pretty serious faults. I have had it stay running when the key is removed. I am to the point where I don’t touch anything electronic on it.

I wish you luck.

I have a 2009 Sierra.  Also a 2008 Suburban 2500.  So I'm a tad familiar with these.

Whenever things get funky with the electronics, the first thing I do is disconnect the battery for 30 minutes for a "re-boot."

If that doesn't work, I check for loose battery cables and grounds.

Then I start looking at other possible causes - fuses, etc.

I'm a bit confused as to what's going on here..

Honestly, I don't know what you mean by "eject mode."

So your battery was dead, you replaced it, still didn't start and the next day the new battery is dead and you're reading 5 volts at the terminals?

If that's the case, I would disconnect the battery and charge it while not connected to the truck.  Then reconnect it and see what happens.

I had a similar issue with an 08.   I drug all the CD's out with a pocket knife and ended ejecting forever.  

Get some MP3's and a bluetooth thingy old man.  

Also clean and make sure your connections to the battery are tight.

Do you have a multimeter?  If so, pull the radio fuse and find out how many amps is pulling while the truck is off. If you see any significant draw, that’s your problem.

Once battery is charged , and the battery is tested as good, remove the positive and negative cables from the battery , turn key on, touch cables together for 30 seconds to completely drain the electrical system, turn key off.
Reconnect battery and see if that fixes the issue.

120 month financing.
Do it.

Funny to read of this on another truck.  Thought mine was unique.

Bad battery, went dead awhile back.  First time, put the charger on it, corrected and fired it up no issue.  Thought I must have left someone "on."

A couple weeks later, same thing.  Charged it up.  Got in later, fired it up, backed up and noticed the only gauges working were the speedometer and tachometer.  None of the other gauges worked.  Shut the engine down and the radio kept playing (it's set up that way.)  But, when I opened the door the radio should have shut off and it did not, it kept playing.  Gauges not working when they should and radio working when it should not.

Got out he scanner, hooked it up and it would not connect to the computer in the truck.  Hell, the computer was working or the truck wouldn't start up and run, but the scanner would not connect and indicated a computer issue.

Got to doing some reading on the computer and looking at some you tube videos and ran across some info about issues with relays in the fuse boxes.  My truck is kind of simple so there are no power window/power lock relays in the fuse box on the side of the dash on the driver's side (one article indicated an issue with a door module relay).  A guy said he got to randomly pulling relays out and putting them in and his screwy electrical issues went away.

I don't have those power door modules so I went to the big fuse box on the driver's side fender well under the hood and began pulling relays and putting the back in.  Pulled all the relays (truck not running, key switch off) and put them back in one at a time.  Went back to the cab, fired it up and all the gauges worked as they should and the radio would turn off like it should.  Hooked up the scanner and it could connect/communicate with the computer like always.  But it showed a butt load of electrical communication errors between systems.  Went through and reset all of those and went back out to shut the hood and noticed the tag on the battery said it was two months short of 7 years old.  Went out, bought a new battery and no issues in the last two months.

Good luck.  Electricity does funny shit.  And the more complicated the engineers make an electrical system the more screwy shit it's capable of doing to make your life worse.  Key off, pull all those relays one at a time and put them back in.  Put a new battery in it and see if it's fixed.