Quadzilla Eats Batteries

In just one hour, I changed clothes, found my overalls, wormed into my overalls, removed the battery, drove to Autozone, argued with them, obtained a new replacement battery (for free), drove home, and installed the new battery.  Sometimes, I impress myself.  This is the third battery I’ve replaced on quadzilla.  The top-of-the-line 7-year batteries always last right at 2 years, and they always test “marginal/good” and don’t want to replace the battery.  (and they always quit when the first really cold spell hits)  My theory is that my charging system is not quite right, and something is draining my battery while the key is off.  In spite of this, everything is OK with a fresh battery.  (I’ve tried to resolve the root issues, and can’t figure them out)  If anyone has any ideas why my charging system only puts out 13.8v (should be 14.8v) let me know.  I’ve replaced the alternator (with regulator) with no change in performance.  The only modification I’ve made is relocating the jump-start terminal, adding a 2-foot length of #8 wire to the alternator’s charging wire.  I’ve jumped across that wire with a jumper cable and the voltage stayed the same, so I don’t think that is the problem.  I’d think that if the voltage-sense circuit had a bad wire (increased resistance), the regulator would overcharge the battery.  HellifIknow.  I guess I have 2 more years to figure it out now…