How long does the cooler stay cool when unplugged?
This is very dependent upon conditions. Koolatron coolers are extremely well insulated and will provide many hours of cool protection, even when switched off. Try to keep the cooler in the shade. Instead of leaving the cooler in a vehicle overnight, use an AC adapter which converts standard 110 Volt AC power to 12-Volts DC and plug the cooler into mains power when not driving.