Use the mains adapter as often as you can. Then your batteries are fresh when you need them.
Mains adapter
Several timeout functions may be set to preserve battery power (and reduce temperature) in the Nor150. Different settings are therefore available for Battery and External Power (Mains) operation. The Backlight and Display picture generation takes some power. Tap on the display to get the picture back on the screen after these timeouts.

If the instrument is left unattended and unoperated, it will switch itself off after a predefined time. However, this does not apply if the instrument is measuring (including being paused during a measurement). The automatic switch off feature may, however, be disabled if required for long-term monitoring purposes.

An Autostart feature will force the instrument to continue a measurement if the operation of the Nor150 was terminated due to a power failure (or empty battery).