Nimh v Alkaline AA batteries in atomic clock

My Eneloops ring in at 1.350v no load.

My alkalines ring in at 1.618v no load.

Lithiums ring in at 1.8v no load. Courtesy HKJ at Comparison of AA battery chemistries

The manufacturer says:
Indoor Displays: Use alkaline batteries. Overpowered or underpowered batteries may cause loss of indoor readings, missing segments, dim display etc.

Not sure if lithiums would be considered overpowered batteries in this low drain application. The manufacturer gives the OK for lithiums in the outdoor sensor/transmitter if the temperature is below –20F. Their exact comments are:
We recommend alkaline batteries for the transmitter.
You may choose to use lithium batteries for temperatures below - 20°F/-28.8°C.

At the end of the day, I might close my eyes and try some lithiums. I have approval from my inner cheapskate. :slight_smile:
Right now, I have alkalines installed with a 2019 wrapper date (6 years ahead of the installation date).