Lift the battery out of the PRAM battery holder.

What I did to free the PRAM battery is I broke the plastic battery holder identical to the circled one on the other side of the PRAM battery, then I was able to free the PRAM battery. I couldn't get the PRAM battery to budge without breaking the holder.

Don't be worried, breaking the plastic holder won't cause much damage nor will it hinder the ability for the PRAM battery to stay in place. Only break one holder, though.