turtlebot3 is not functionnig on his bettery i don't undrstend the problem

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i build the turtlebot3 burger all the parts are connected by the manual .the respbary3 is with rasberian. i did all the setups as they written in the e-manual. when i conacet the respbary3 to a power source through the mini usb and all the components work but when i turn the turtle on by the battery the respbary3 does not turn on their is a red light on all the time and the green light flashing. in the opencr the only lights that turns on is the power and the state is flashing. i don't understand whet is the problem.