The Bosch CORE18V Compact Battery 2-Pack features two next-gen Lithium-ion batteries that each keep the power and runtime, while losing the weight. The GBA18V40 single-layer battery features advancements in design to reduce resistance and increase efficiency, to improve the performance-to-weight ratio of tools used on the jobsite all day.Engineered with 21700 cell technology, the battery matches the power from the original two-layer 4.0 Ah battery with improved performance per cell. Bosch engineered the exclusive CoolPack 2.0 technology to manage the heat of the higher power-density cells, and it provides better cooling than the previous-generation CoolPack system. CoolPack 2.0 cools the battery 15% faster than previous 4.0 Ah double-layer versions. This new-gen CORE18V still features compatibility with Bosch 18V Lithium-ion tools and chargers.