I have the same problem, slightly different parameters. Factory battery didn’t offer even 90 minutes of run-time and would suddenly die, so I wanted to replace it (laptop was purchased from OWC). I also managed to wrestle a replacement battery from them as this used laptop did NOT provide the battery life they said it did…. but it was a HUGE fight… System Reports “Service Battery”. They had me chase my tail for a while, making me run that useless coconut battery app… so I jumped through all the hoops they required (hoping I’d just go away) but I’m a tech and persisted through it all. The replacement battery shows 1% charge… I think it came with about 5-9%, OS 10.13 shows AC 85W adapter is connected, I can see ALL battery info in System Profile, but the NEW battery is “Not Charging” and “Replace Now” message is also present . No SMC, PMU or PRAM etc resets change the status. The AC adapter is orange to suggest the battery is charging, but it never does. Either OWC sent me a door-stop instead of a new...
After removing the display, I also removed the 3 screws for the processor fan, disconnected the power connector for it and set the fan shroud aside. Disconnecting the remaining cable (similar style to 1 of the cables for the display) that is in the way of the RAM chips is all that's left to do. I was then able to access and quickly remove the two Apple-provided RAM chips, and replace them with 3rd party RAM. Turning the iMac on its side, so that it's in a position where you're physically putting the RAM chips DOWNWARD into their respective slots is the best way to go about uninstalling and reinstalling the chips. Using a narrow but long'ish plastic spudger tool is the best way to defeat the spring-tabs which hold the RAM chips in place. After removing the LCD display, changing the RAM is about a 10 minute process!! And I'd SURE prefer not to remove all the parts and risk damage to the iMac via the standard procedure listed. As per usual, take your time and work gently :-)
After removing the display, I also removed the 3 screws for the processor fan, disconnected the power connector for it and set the fan shroud aside. Disconnecting the remaining cable (similar style to 1 of the cables for the display) that is in the way of the RAM chips is all that's left to do. I was then able to access and quickly remove the two Apple-provided RAM chips, and replace them with 3rd party RAM. Turning the iMac on its side, so that it's in a position where you're physically putting the RAM chips DOWNWARD into their respective slots is the best way to go about uninstalling and reinstalling the chips. Using a narrow but long'ish plastic spudger tool is the best way to defeat the spring-tabs which hold the RAM chips in place. After removing the LCD display, changing the RAM is about a 10 minute process!! And I'd SURE prefer not to remove all the parts and risk damage to the iMac via the standard procedure listed. As per usual, take your time and work gently :-)