Need a battery for Dell Laptops/Notebooks with the following model numbers: 1520, 1521, 1720, 1721; Vostro 1500, 1700? BTI has you covered with our premium 6 cell LiIon battery. This product has been engineered to meet or exceed the original manufacturer's specifications and replaces the original Dell part numbers 87-22S8S-4EC, M22BAT-8. All BTI batteries are manufactured and tested under our stringent quality standards and come with an industry leading 18 month manufacturer's warranty. BTI... True to the original.