The battery on my 2003 blazer 4.3 vortec keeps draining.. it completely killed one battery and I'm going to pick up a new one tomorrow n I have to figure out what' doing it so I don't have to keep unhooking the battery terminal cause at some point no matter how careful u are you'e going to forget it sometimes and miss work or be stuck somewhere.. I just got a new job so I can' afford for this to happen.. someone please help walk me through everything I need to check to find the problem.. thanks in advance

 

Every now and then, I'd come out to my battery drained the last year of the life of my battery. I suspected that there was something funny going on with the retained-accessory power system but I could never be sure.

 

I would suggest as a troubleshooting measure, start pulling a single fuse for the period of time it takes to drain it and see if pulling a fuse will stop the drain of power. If it is dead again then insert the fuse back in. This will isolate the system/circuit so you can start diag on it. Its simple and doesnt cost you a penny

 

95teal4x4 is on the right track. Parasitic drain tests show which circuits are draining the battery by measuring the drain and pulling fuses one at a time until the meter reads .05 or under. You tube has many video demonstrations.

 

If you have a factory radio in it, I will guess and say if you pull the fuse for the clock radio memory, thats your drain, I have seen several blazers do that but like everyone else says do a parasitic draw test plucking one fuse at a time. Also watch using an expensive milliamp mA meter when testing, I have smoked-burn up a few in my life haha

 

X2
The radio is famous for doing this in the late model years. My 02 with the later double din radio did it.
There are a couple videos on YouTube showing how to find a parasitic draw with a multimeter.
I found my problem after watching one.
Since the late model CD player radio is expensive and a PITA to replace because of security,
I pulled it and spliced an on off switch into the B+ wire.
Think it is the red one. It's the only one that is always hot. I put a cheap switch in the glove box loose.
Mine only did it over a couple day period so I only shut it off if I'm not going to be using it for a while.
Funny thing is that was 2 years ago and now I can let it sit a couple weeks with the switch on and no problem.

 

A lot of systems in a vehicle can cause a parasitic drain Esp. any thing with a memory and actually that's normal. all cause somewhat a drain on the battery.
Besides a draw test do the basic tests of charging systems, weak or corroded battery cables and or terminals, weak or dead cell in the battery Ect.
The memory in the radio such as the clock and station set shouldn't draw a fully charged battery down over night.
I own four vehicles all have radio memory's, three of them have computers and Ect. Some of them sit for months on end with no ill effects. But my charging systems, battery's Ect. are in good shape

 

That's true, but the late model S-series have a problem with some defective cd/radios that draw too much.

 

Check the vanity lights in the visors.

 

And the level switch for the under-hood light. Don't ask me why.