Stop in for a cup of coffee

I asked sales person at Batteries + why replacement batteries don’t last as long as factory installed ones. He said when a vehicle is new things work easier and takes less battery energy.
Yep, age, weathering and environmental conditions slowly degrade the electrical infrastructure of a vehicle such that corrosion wear increases resistance within the system and impedes electrical circuit efficiency. Even just a little corrosion on the contacts in every electrical connection changes the current flow and reduces the effective voltage getting to components creating more impedance resulting in more draw from the alternator to keep up.

All of which reduces the available power to maintain the battery at full charge.