Battery life estimation broken?

Hard to tell. It could be just more accurate and closer to the reality now. Or the battery gauge calibration got reset during the firmware update (which happens frequently) and needs to be recalibrated by a few full charging cycles. Or the watch momentarily draws more current than usually (i.e. downloading some additional components, like fonts, and diverse tables), which is also common after a firmware update. Test it, and see how long it holds.

I found old photo form March and the battery estimation was 45 days! No settings has been changed since then.

Yes, I believe you. That's why I listed several possible causes

I'm testing just now, and would be able to tell after several days...