New iPad slow charging with 10W charger

Compared with my iPad 2, charging the new iPad with 10W charger is really slow. I have taken 6 hours of charging went from 9% to 81%. I didn't run any app on the iPad. It ran battery life down quickly and after 6 hours it was only at 35% and started at 10%.The new iPad sports much larger battery. It has a 42.5-watt-hour battery, and the iPad 2 just has the 25-watt-hour Lithium-Ion battery. The