Battery sign X Not Charging after RAM Upgrade

Hi, Just upgraded my RAM and Installed a SSD into my macbook 2009. Whilst doing the upgrade I didn't take out the battery from it's connector as I never thought it was necessary. Now unfortunatley my mac does not charge and magsafe stays on a green light. The battery does not get recognised and has an X sign over it or sometimes shows 0%.

After seeing the problem I have done the following:

-SMC Reset - Did not work

- Tried New Battery - No difference

Any ideas how I can solve this issue?