Bosch GBA18V40-2PK 18V Lithium Ion 4.0 Ah Compact Batteries (2 pack) 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.