Renault Laguna Jumpy in neutral no power feels like its going to stall Help?

I have an 00, X Reg Laguna Sport. It was driving ok but Dead batterie changed batterie and now when it is ticking over the engine jumps about like a box of frogs. It settles at 2000 revs but when it drops back down it goes Crazy again. Also no power when changing feels like its going to stall. Very sluggish at pulling away but then hits the revs after jumping around like its gonna stale. Just Brought car so not too happy just got new batterie not cheap and