When the battery capacity drops below a pre-established threshold from full charge , the vehicles enters charge - sustaining mode .
The Volt 's control system will select the most optimally efficient drive mode to improve performance and boost high - speed efficiency .
When the battery capacity drops below a pre-established threshold from full charge , the vehicles enters charge - sustaining mode , and the Volt 's control system will select the most optimally efficient drive mode to improve performance and boost high - speed efficiency .