I thought all "battery life" mode does is turn the screen off after 1 minute of inactivity, rather than optimize the whole computer for better battery life
I would assume that on newer computers it would tell the CPU and GPU to hold off on bumping up to higher speeds so easily.
"Your MacBook Pro is preset to automatically reduce its processing speed during
periods of light processing activity when using battery power, thus reducing power
usage. The setting that determines this is the Normal option in the Optimization pop-
up menu of the Energy Saver pane of System Preferences. During periods of high
processing activity, your computer will automatically switch to a higher processing
speed. To conserve the most battery life, choose Better Battery Life from the
Optimization pop-up menu. Be aware that choosing this option may affect your
computer’s performance. To set your computer to use its highest processing speed at
all times, choose Better Performance."
From the document "Macbook_Pro_Users_Guide.pdf" from the Apple Support Website.