Suggest buying a DVM (digital Volt Meter) and plugging it into the cabin power point, permanently if not being used for anything else, and monitoring the voltage while driving normally, coasting etc. If the battery SOC is up around 80% then the DVV will show 14.5/14.8V on overrun and ~ 13.0/13.6V with accelerator pressed, if the SOC is down around 75% then its more than likely that the charging rate is 14.5/14.8V under all driving conditions. My over 7.5 year old Polo petrol 65BHP (Original) battery SOC has often been down around 75% but stop/start never failed to operate any time I care to use it. The max SOC is 85%. VCDS 10Friday,05,June,2026,10:45:58:555 42,715 kms/26,542miles. IDE01834 Battery voltage 12.193 V IDE01836 Battery current -4.950 A IDE01839 Battery charge status 77 % IDE01841 Battery internal resistance 7.6 mOhm IDE01842 Usable battery charge 28 Ah IDE01948 Battery internal resistance not normed 6.0 mOhm IDE07681-MAS06086 Battery total charging throughput-Total re-charge 3890.7 Ah IDE07681-MAS06087 Battery total charging throughput-Entire energy throughput 4091.0 Ah Battery Capacity 59AH.