Wired battery doorbell stopped charging

My wired battery doorbell stopped recharging since a couple of days. Normally it recharged from 87% to 90%. Since couple of days it stopped recharging.
Already shut down the doorbell and restarted, did a factory reset but nothing helps.
Also measured the output and it shows 14,5V but it has always worked with this.
I saw there was an firmware update beginning of June so I wonder if this can have an influence?
Dies anyone has other suggestions to solve because this is really annoying.