They discounted dozens of products and saw great success — so much success, they doubled it to two days. Then four days. And now, it's no longer just Amazon Prime Day — it's the biggest sales week of the entire summer,

Milwaukee’s two-pack of high-output batteries is another great deal, currently an impressive 50 percent off—a savings of $150—at Walmart. These 18-volt batteries are compatible with over 150 M18 cordless tools and have a 6-amp-hour capacity. They also come with overload protection and a three-year warranty.

Walmart has launched its own summer sale event to counter Prime Day. Only some deals are actually worth grabbing.