macbook pro 2012 battery charging issue

Battery wont charge when connected to power. Displays 'Not charging' and the magsafe is illuminated green.

2012 Macbook pro, non retina, running latest version of El Capitan.

Cycle count on the battery is only about 200, condition shows as normal.

So far I have tried the following:

Reinstalled the OS from new.

Disconnected the battery and reconnected it.

SMC reset

The only thing that appears to help is the SMC reset. I power off, then hold down the Shift-Control-Option keys and the power button at the same time for 4 seconds. I release them and the magsafe will turn orange and begin to charge the battery.

However if I press the power button the magsafe immediately switches back to green again and the system boots up.

Thanks for your input