Recognition on Auto lead battery

I must change the recognition of automobile led battery, replacing batteries on BC7 SUBARU Legacy LSi US model into into fully charged D type from 6 years old Europe standard one with the sign of enough specific gravity of electrolyte inside.
20mm lower height and with the same size terminal diameter and taper angle on plus and minus promptly, interchangeable if lack the height is compensated by some adapter.

Though I have a recognition that the automobile battery should rotate the ring gear outside of flywheel and give some spark at initial stage of motor starting phase. Then once the motor was started, all the electricity necessary for activating the car should be supplied from the alternator rotated by the motor power, so the physical performance of the lead battery has no direct effect on that of the car itself. The performance of the alternator has the dictator of an electric supply, if once the motor started.

But this perception was completely changed by the eye opening improvement in every performance of BC7 Legacy after the replacement of the batteries
Even on this D type battery, once deserted after 3 year use by my son with fully discharging condition, and I repaired it with special charging method, Trickle charging act, small current with relatively high voltage and pulsing circuitry.

Conclude I that the absolute reduction in capacity in automobile led battery does harm on every performance of the performance of the motor.

BOSCH 120A alternator is limited at 13,5V with only 2 terminals plus B and for charge lamp, DENSO 70A one in BC7 Legacy has the limited at 14,5V, I think this difference of 1V has much to do with the life of the Automobile Lead Battery, especially the car was used in relatively slow traffic speed conditions.