The Milwaukee M18 HNRG Battery Twin Pack, contains the following:

2 x 18V M18 HB12 HIGH OUTPUT™ Slide Batteries. Provides 50% more power and runs 50% cooler vs M18 REDLITHIUM­™ HD battery packs. The massive increase in power elevates the performance of the entire M18™ system and drives the next breakthrough in M18 FUEL™, delivering the power of a 15A corded product.

It delivers fade-free power and runs substantially cooler through heavy applications, allowing tradesmen to push their cordless tools harder and longer than ever before. It is the best performing cold weather pack ever made, providing increased power in extreme cold weather conditions (below 0°F / -18°C). Provides the most work per charge of any professional power tool battery in the industry, driving full corded replacement on the job site.

They also feature a fuel gauge to display their remaining charge.

1 x 12-18V M18 & M12 Rapid Charger that is up to 40% faster, reducing downtime and maximising productivity. The charger accepts all M18™ and M12™ batteries, providing an upgrade for both systems. Featuring REDLINK™ Intelligence, it communicates directly with the battery to monitor cell voltage, temperature and charge status to optimise the performance and extend the life of the pack.