I'm sure the I(t) curve is just AC coupled, i.e., offset to be drawn around zero. The "zero" is likely, according to the first graph, around 150A, so the Y axis of the second curve ranges from 120A to 180A, not from -30A to +30A.
This amount of current ripple seems understandable and normal, it's a rectified AC generator. The battery won't care about this ripple.
Voltage ripple cannot be given because it's a property of the complete system and depends on the ESR of the battery. Current ripple is the property of the alternator, and the voltage ripple is then easy to calculate by U = R * I, given the R of the battery is known.