MacBook Shows X sign battery, but works off battery

Hello everybody my first post here. here is the story. i got a Macbook mid 2009 A1278 with the 820-2530 Motherboard, i bought it second hand with short battery life, i bought a knock off replacement from a local store. worked but the battery dies unexpected always on 40-50% but kept reading the battery (percent and if there is one), want back to the store and they asked also the computer to see if it really was a battery issue, turned out it was. After a day i called them back and i asked if since the issue is confirmed can i have my macbook back since i was using it for xcode on college and wait till a new high quality replacement battery arrived, they said yes, i got my mac back BUT it was showing an X icon on the battery, no green LED indicator on the side, nothing. excpept when i unplugged the charger(with green light never gets orange) macbook was still getting power even though it reported it has no battery, i was confused plus the LED on side didnt work. so i got a call from the store saying the new battery arrived and i should go there with my laptop to install it. i went and upon plugging the battery i got green light on the charger, no green battery LED status, with the new battery.i boot it up, removed the charger and the mac reported no battery and a green light. the battery was good since they had an A1278 next to me for testing the issue. so:

TLDR

Macbook Shows x sign on the battery, doesnt charge/turn orange, no green led battery LED activity, BUT if it turns on via charger can use battery power with “no battery installed” NVRAM/PRAM and SMC reset was performed multiple times with no changes

(i just hope this is not an SMC issue)