When building a robot a regulated power supply is very important to give the controller a good stable 5 volts. Normally a 7805 or better is used. Which is a lineair supply and is very 'proven technologly'. Except it is not very efficient. When used with a battery pack all the volts above 5 are burnt away.
Solution for this is using a switch mode power supply, (buck and or boost regulators). These have a much better efficiency but are less common and therefore much more expensive. Also the ones I found can delivery less than one amp.