iMac 2011 startup issues & x8 beeps
I like to remove all RAM and then power up just like you did. If there are severe hardware issues - the system often won't give you the correct diagnosis. Now if this works, there still could be hardware issues:


https://support.apple.com/en-us/HT202768


Then I put in one RAM stick and try rebooting. If that doesn't work - reset NVRAM one time (hold for two beep cycles) and then repeat the power off / power on. You've probably done all you can and will actually need to get the hardware repaired or just pieces reconnected internally. The clock batteries aren't needed for successful boot - then you can set the clock as needed - they're nice to have and not required.