Doorbell battery not charging from solar panel

This solar panel has worked perfectly for nearly a year now, no need of manually charging battery, until now. Alarm battery low. Charged the battery manually to 100 %. All working, except not charging from solar panel. I measured a voltage about 4 volt from solar panel without battery connected. Is that correct voltage for charging the battery, and if so, why is it not charging?

Hi @Asbjorn. For this concern, it may best best to follow up with our support team. They will be able to analyze the battery history and narrow down why this is happening. Please give our support team a call at one of the numbers available here. We’re taking additional steps to protect our team and help reduce the spread of COVID-19, so this has resulted in longer than normal wait times. If you are outside of the US, please read our response to COVID-19 here to see how to contact support.