It is always annoying when something does not work or when logging in does not work.
In all probability, the ADB-15 is not broken but something else is wrong.
You can try/check the following to register the doorbell:
Do not use rechargeable batteries in the indoor unit, it works with normal batteries that are 1.5 volts each. Rechargeable batteries provide 1.2 volts each.
Put the batteries in the indoor unit and then the flat button cell CR2032 battery in the outdoor unit, then press the doorbell within 10sec.
If you have any additional questions, you can always contact us via this website.
Please mention the question or complaint clearly so we can serve you well.