Here's what other sites are saying:
Mammut X-Pack Battery. Small, compact and high performance, these are the key features of the 4,400 mAh lithium ion battery for the X-Sun headlamp. The battery's two-cell lithium ion technology is distinguished by optimal energy density combined with minimum weight, low self-discharging of the cells and high temperature resistance in cold conditions. The X-Sun is perfect for any activity of your choice, while replacement Mammut batteries ensure you are always equipped with sufficient energy for any tour. Technology: lithium ion. Capacity: 4,400 mAh, 3.7 V. Number of charging processes: around 500. Operating temperature: 0 degrees C - +40 degrees C / 32 degrees F - +104 degrees F. Weight in g ca. 140 g; [lbs] 0.31; [oz.] 4.95
- Tahoe Mountain Sports
It's always a good idea to take an extra Mammut X-Pack battery for your X-Sun headlamp on any of your adventures. Sure, the X-Sun's included battery lasts for up to forty hours, but you don't want to be in the middle of nowhere without a light. This rechargeable battery will last for up to five hundred charges for five-hundred adventures.