I don't have the HP option and at delivery had to point out to the salesperson the new car delivery crew left them in the springs. Count yourself lucky if they read the instructions that come with the car.
Hydrogen is orderless.
Hydrogen sulfate smells like rotten eggs and is created when a battery is overcharged.
What readings are you getting on your voltmeter?
I have Interstate on the 21 Mach 1, 71 GTO and 69 Corvette. On the two older cars I replace the battery at 8 years to be safe. I keep all 3 cars on a battery maintainer whenever they are not being used.
Have you tried locking the car and placing the key fobs a significant distance away from the car?
My 21 Mach 1 battery lasted 4 years replaced with Interstate and reset battery monitor at time of install.
When not used for a period of more than a few days use smart trickle charger from Deltran.