You have a good performance and I am never one expired.
I bought in December 2011 a KMX Erni from Fisher Price, that was still in their original packaging and sealed. The Erni was included GP AA batteries packed inside the battery compartment! Been expired in 2008!
The Erni worked fine with it. But I replaced them with new ones because I use it rarely. The old GPs did even a year their service in the heating control thermostat Honeywell HR40 my central heating. In the study I did the last until now been replaced recently.
My ordered in November 2013 GPs AAA are dated 07/2020.