It has three functions. It can be used, 1) as a replacement, 2) as a spare, or 3) as an extra pack to carry with you when you ride. When you take an extra pack along, simply slide out the old one when it's lost its charge, then slide in the fresh pack to extend your range. 1 year manufacturer's warranty included.
* The X-Treme Laguna has undergone a name change. It was formerly known as the X-Treme Santa Cruz and the X-Treme Santa. This battery fits those models as well.