Battery suggestion

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i am using this 4 dc motor(100rpm) and 2 l293d motor drivers…if i want to run it for 15 minute.what is the best option for me?i dont want the robot to get too much heavy…

http://letsmakerobots.com/nod

https://www.robotshop.com/letsmakerobots/node/28427#comment-72880

Here’s an excellent write up (by myself of course) about batteries.