I bought and unboxed my DJI mavic pro drone yesterday. Took out the battery, charged th battery and the remote controller yesterday. After 3 hours of charging!, the remote controller shows '100 pct' battery on trying to turn on, but the mavic pro battery won't turn on at all. The leds won't turn on/blink at all. It's totally dead. Tried pressing once and then pressing again for 2-3 seconds. Nothing happens. LEDs won't respond at all. Please help!

When you were charging the battery did the led's blink?

If you press the button once It should show you the battery status, 4 leds = full etc. To switch the battery on you have to press the button twice... I also want to know if there were any blinking leds during charging!

some times if you do not push the button correctly ie either too long or too short between first and second push then it will not register.
Push once and then quickly again and hold and let go - hope this is all thats wrong -
Does it not work with all batteries or only one?

warranty of batteries is 6 months and 200 charging cycles.. if that is new, call dji for swapping ng battery

What Mari said is correct, please try to press the power button for once, check the LEDs, and also try to charge the battery, see if there are any blinking LEDs. You may need to send the battery in for diagnosis if the LEDs are always off.  You can refer to the link below to contact the Support, they'll create a case for you. http://www.dji.com/support