Blazer won't start
 

Aight fellas maybe someone can help me out. I got a 2004 chevy blazer, now I've checked the starter and alternator and they both checked out to be good. The battery was replaced so I got a new one. All the fuses were checked as well and 2 were replaced. The car won't start on her own, I need to jump start it. When its cabled up to my wife's van it shows normal battery life but the low battery symbol still flashes in the dash. When I disconnect it from the van the battery immediately goes lower and the car sounds like it's struggling to stay on. There's no check engine or any other light in the dash on other than the battery. I connected it to them code readers and no codes came up. Can someone please help me with this? I'd appreciate the help and thanx for hearing me out fellas!