Citroen C3 1.4HDi 2003; My car battery keeps dying and i'm not sure why? Do you think investing in a new battery is the best answer? Also when i'm driving, the car sometimes cuts out when i'm changing down gears, i can restore it by bringing out the clutch but sometimes the power steering becomes heavy and it can be quite annoying? Please help me...

I've already tried charging the battery, but if i leave the car not running for a couple of days, it dies again and needs charging...