Using the mac with an external display

I have an external display which I use regularly and an external keyboard/mouse combo that i've paired to my mac. I don't always need to use the display as an extended desktop. There doesn't seem to be an option to close the lid and work using only the external display, unless the charger is connected to the macbook. This means that I have to have the charger connected at all times. I understand that this is a practice discouraged by Apple as it can impact the battery life of the macbook. The only other option seem to be to keep the displays mirrored, and then to turn the brightness of the retina display to zero which switches off the display. But if i close the lid, the system goes into sleep mode. This is counterproductive. Is there a way around this?