Catalytic converter fault on 206 xsi what's causing it?

Recently my 206 has been playing up starting from one day struggling to accelerate which was resolved when turning off the engine, eventually this same fault occured including fluctuation in revs and juddering with also the catalytic converter fault coming up on the dash, when I tried turning it off and back on again the battery decided 2 die sometimes. Once being jump started it runs as normal 4 a while untill the cat fault re-occurs, and battery now randomly runs out when left a while? Any ideas?