Unrecognized battery after HDD and RAM upgrade

After everything done, following your guide. The mac is working properly, except for the battery, that is working, as i can sometimes turn on the mac, with a loud fan noise on battery mode.

With AC power connected it runs good, but there's a cross on the battery indicator, indicating that there no battery.

How can i solve this? what steps should i follow exactly to make my battery recognizable again?

(tried already some solutions, on plugging/unplugging the battery connector with and without AC power plugged in)

Thanks in Advance