I have a 02 blazer zR2 and have been having problems lately. Towards the end of December i replaced the original battery as it lost its cold cranking power and wouldn't start on really cold days. a couple of days after installing the new battery i went to start it and it had absolutely no power, not even enough to unlock the doors. found that the problem was the negative battery cable was loose so i tightened it. truck started up fine after that. however, after about 2 weeks i started it and it seemed hesitant, after i started i shifted in gear it semmed ok but as i pulled out of the parking lot all the gauges started going crazy and all the warning lights would come on then go off one by one then all come on again and slowly shut off. I got the truck home and when i shut it off it killed power to everything and wouldn't even release the key. i had it towed to my mechanic who inspected the alternator and the charging/electrical system but found no faults. he took off the battery cables to inspect them but said they are fine and when he reinstalled them the light under the hood came on and it regained all power and started right it. 2 1/2 months went by with no problems then out of the blue it happened to me again. I took it to a GM dealer who inspected it again and said they found no concerns, so they told me to take the battery back. However, the store i bought it at said they won't replace it under warranty because when they charge the battery it tests ok. I told them i'm not surprised as it has never lost power while being driven and after it's little episodes the battery gauge always reads normal. Just wondering what to do next.

 

Try replacing your battery cables and making sure the connections are clean. Even better, upgrade to the "big 3" and upgrading your battery cables.

 

I agree with the big 3 as well. And if not that at least the ground at the battery. Do you have any amps, lights, anything that will use power. It might not be draining you battery but using too much of it while the vehicle is running. My get a load test done on your alt too.

 

The only thing in my expierence that causes crazy gauges on blazers is a loose battery cable. the cables could have excess resistance in them or the cable mounting surface could be corroded or rusted, I would replace the battery cables and use new bolts and clean the cable mounting surface before insallation.