If you battery light has come on it alternator not charging it won't be the battery, battery problems are slow lazy starting or quickly discharging and going flat by just listening to the radio. You got to remember the mech on these windows are at least 12years old now and after constant use will wear. Try dry silicone spray on the runners that locate the glass and see if there's an adjuster in the door to compensate for the wear I know rover have something similar. Also if your engine is struggling to idle when under load maybe an earthing check to make sure your body/engine has a good earth maybe an earthing kit.