This is a migrated version of my Wordpress post, written on : 8 Mars 2015
I used the Pi as a brain of an autonomous car toy project, for such project, autonomy is alway a key factor that must be considered. So i did some researches to find an efficient way to power the Pi with battery. In my project, i used 4xAA batteries as power source ('cause those ones are very popular and easy to find).
To save the power, my suggest is to use the PI A+, this version of Pi is the less energy consuming in its family. In headless mode (without HDMI,camera, Idling in the command line), it requires around 100mA - 120mA (with or without an USB wireless attached for network communication).
The first thing you need to do is turn off the HDMI output, this can help you save about 20mA. Notes, without the HDMI, you can only access to the Pi via network using ssh (that is, you need to configure the network to work with ssh before turning the HDMI off).