If the SunEye battery level indicator on the device: Sun icon>>Tools icon>>"About Solmetric SunEye.." indicates 0% charge even after "charging", it is likely that the charging circuit is not operating correctly. Seldom is the battery actually the culprit*. Before returning your SunEye for a battery replacement: 1. Install the latest version of SunEye software onto the device . Software downloads page 2. Perform a Hard Reset . 3. Keep SunEye connected to the AC wall charger and wait 15 minutes. Check battery level and if not  gaining charge, call Solmetric support to arrange for repair. *Please note that the AC wall charger is the best way to charge your SunEye. USB charging is very slow and will often lead to poor battery performance that will make it seem as if you need to replace the battery. This condition is very often resolved by charging and "hard resetting" the device (see link above) .