The drinking alarm is battery operated.
The battery is replaceable.

The installed battery is a high quality lithium battery: CR 2032.
In normal use, it holds about 1000x
It is easily replaceable and costs depending on the source of supply
between € 0.25 and € 1.00.
They unscrew the milky lid of the drinking alarm
just disconnect and replace the battery.

Unscrew the lid

... and change the battery