Might be a faulty super capacitor. This seems to be a common problem. Although the last I heard this problem's been fixed unless you have an older station. The super capacitor supplies power during the day with the battery as a 3 source. If the super capacitor goes bad then the battery kicks in. I remember someone telling me a while back if the battery even a relatively new one is charged and depleted day after day it's ability to hold a charge diminishes.