The ZENN has a "fuel" gauge that works like a regular car. When it is down to about 1/8th of a tank, there is a warning sound and the display starts to blink. With the cars we have driven, there is about 5-10 miles left when this happens.

If you do not recharge, the ZENN will let you know it is starving by running slower and slower. You can limp along for awhile before the batteries have no more to give. It is important to recharge the batteries immediately since completely discharging the batteries can lead to permanent damage.