NiMH Battery (gWind™ Wirelss)The internal batteries of the gWind Wireless are continuously charged by a small solar panel integrated on the transducer arm, and have a life of around 3 to 4 years. But when the time comes to replace them, they can be easily replaced with this NiMH battery.WARNING: This product can expose you to chemicals which are known to the State of California to cause cancer, birth defects or other reproductive harm. For more information go to P65Warnings.ca.gov.