My spare(looks newer) key fob needs a new battery if I just put new one in will it conect OK to car straight off? 

Yep. No need to re-code, it thats what you are worried about. As long as it works/worked prior to battery swap and battery was the only fault, it will be fine. 

Do you know how to do the battery? Its not hard but you might want to go to say, Timpsons or somewhere similar, if unsure.

Ta thought it would be fine

Will it not need the remote part to get re-aligned with the car as any memory of that part will have died?

 

Engine immob part will be okay though.

I changed the battery on my fob without any issues. Instructions are in the manual.