Grade B batteries use lithium cells that have slight variations in their specs than the ideal. These cells are sold wholesale to manufacturers for pennies on the dollar. When carefully matched with other, similar cells, and a good BMS they can perform the same as a Grade A battery but will not last as many cycles. However, the big savings in cost can be a great tradeoff for customers who don't necessarily need a battery that can go 5,000 cycles (which is every single day for over 13.5 years!). Weekend boaters, RV travelers, and others can enjoy all the benefits of lithium batteries for a smaller investment.