Wikipedia says GM programmed the Gen 1 Volt to use ~65% of the full capacity for Electric Mode driving. Your energy usage display photo shows you drove 35.6 electric miles, 9.0 kWh Used. If that’s the normal kWh Used you get for a full charge when you drive beyond battery range, math says the current full capacity of the battery is 9.0/65% = 13.85 kWh, which is ~84% of the original 16.5 kWh full capacity, or ~16% degradation over the years. IOW, it would appear your Volt’s battery has lost some capacity over time.
All batteries lose capacity over time (GM warranty says the Gen 1 battery should not lose more than 30% in the first 10 years). If all cells lose their Ah capacity at the same rate, then they’ll remain fairly well balanced, but, of course, your kWh Used per full charge will decrease. It’s when some battery pack cells lose capacity faster than others that results in larger voltage differences when the battery is depleted... those 96 cell groups are connected in series, so each contributes the same amount of current flow to the battery’s power output. If the cells are balanced at the full charge level, then those cells that have lost more capacity (Ah) over time than the others will, of course, discharge faster, so that by the time the automatic "switch to gas" has taken place, the voltages of those cells will reflect the lower remaining capacity of those cells, and will be lower than the voltages of the cells that have lost less capacity.
All batteries lose capacity over time (GM warranty says the Gen 1 battery should not lose more than 30% in the first 10 years). If all cells lose their Ah capacity at the same rate, then they’ll remain fairly well balanced, but, of course, your kWh Used per full charge will decrease. It’s when some battery pack cells lose capacity faster than others that results in larger voltage differences when the battery is depleted... those 96 cell groups are connected in series, so each contributes the same amount of current flow to the battery’s power output. If the cells are balanced at the full charge level, then those cells that have lost more capacity (Ah) over time than the others will, of course, discharge faster, so that by the time the automatic "switch to gas" has taken place, the voltages of those cells will reflect the lower remaining capacity of those cells, and will be lower than the voltages of the cells that have lost less capacity.
