Sams right but the main thing is before you get to involved with it is to take the battery leads off and re connect them firmly(make them grip)all the clock/lights stuff is by the by the by.I reckon you have a poor battery connection,Take the earth lead off and clean the battery terminal and connections with wire brush/sandpaper any abrasive and re connect firmly,it was ok'ish before you fitted the new batt it should be better now.The cold weather is showing up all the faults,go back to the basic's before you assume the worst.Good luck.
Rich, January 2010