is there any way I can completely disable all acoustic warnings, like low or empty battery, and low recording time left?

The buzzer is output to the built-in speaker or to
the headphones connected via the headphone
connector. The buzzer volume can be adjusted
with “Alarm Level” in “Audio Output” of the
AUDIO SET menu.

Page 156 in the EX1R manual.

RTFM in a nice way. The PDF version is great you can search it.

thanks so much!!