the link you gave showed 18 and 27 (larger or more expensive batteries) core charge;
that sounds normal.
napa stored are franchised (i think) - they have leeway as to how they want to operate

 

As a rule, automotive batteries are all the same core price. There may be exceptions but I can't recall any.

NAPA stores are either company stores or privately owned. Company store pricing is set by the national office, with regional variations, and some discretionary pricing by lower management - store or group level. If a store has a lot of price overrides, many will be increases, not just decreases, to keep the margin within limits.

Independent stores are not actually franchises. They pay a monthly fee, they must buy the NAPA computer system (and pay monthly support) and they must buy and maintain a signage package. There is also a monthly fee. All this is negotiable. In return they get real-time pricing updates, good cost pricing, and most of all a national identity with marketing. They use NAPA pricing but have almost unlimited flexibility with pricing. The store owner can set any price they want. The national pricing is the baseline, with discounts applied as needed to win more business.. Independent store owners are encouraged to adhere to the national pricing.

-Rex - Spent a lifetime in the automotive aftermarket