I have three brands of back up belts, Napa Premium, Dayco Top Cog and Advance 15430. The Napa Premium is notched on the inside, the other two on the outside. Which is better?You should always use a grip notched belt especially when doing around a small pulley such as an alternator.
A notched belt has grooves or notches that run perpendicular to the belt's length, which reduces the bending resistance of the belt. Notched belts can use the same pulleys as cross-section standard V-belts. They run cooler, last longer, and are about 2% more efficient than standard V-belts.