While most manufacturers of 18-volt cordless tools have only recently made the transition from 3.0 to 4.0 Ah battery packs, Metabo is introducing a 5.2 Ah pack to the U.S. market. It has the highest Ah (amp-hour) rating of any 18-volt pack currently available (Hilti has a 6.0 Ah 36-volt pack and other major tool companies are rumored to be working on 5.0 Ah 18-volt packs).
What made this new pack possible was the development of a new more energy dense battery cell by Sanyo (a subsidiary of Panasonic) for Metabo. The new pack is no larger or heavier than its predecessor and is backwards compatible to the company’s other 18-volt tools. It stores 75% more energy than a 3.0 Ah pack and 30% more than a 4.0 Ah pack. Each cell is individually monitored and protected by electronics. To prevent overheating, there is a fan built into the charger to blow air through the pack during charging.
The Ultra-M pack has a 3-year warranty and is currently available with select tools. While the company offers a full line of cordless tools I would expect to see this battery packaged first with metalworking tools such as grinders because that's a core category for Metabo. The 5.2 Ah pack is manufactured in Hungary and can be purchased individually for about $139.