Sudden battery drain (Nuki 4.0 Pro)

[Socio241]

Hi,

I have been using my Nuki 4.0 Pro without Bridge since mid of February and everything worked fine.
About two weeks ago the charge level of the Power Pack dropped from 82% to 18% within 8 hours.
I recharged it to 100% and it stayed on 100% for 4 days. Then within 48 hours it dropped from 100% down to 16%.
Recharged it again, it stayed at 100% for 4 days again (that was 36 hours ago) and is currently at 46%.

I do not use the official Nuki integration, only the hass_nuki_ng. Polling is set to 30 seconds and the debug logs also show that the update is done every 30 seconds.
Any ideas what could cause this?