nrf52840-DK ble_app_uart not working with external power

Hi i am using ble_app_uart example in sdk 15.3.0 as far everything is fine even i added a app_timer for about 20 sec to advertise again but the problem is when i power up using coin cell or li-po battery the device struct, it's not running and i don't know what is happening. How i conformed that it was struct by the help of led4 in the board, which i set in the main function starting and after delay i cleared but still led was on and no advertising when it in external supply. i don't think there is any issue with app_timer but other than something could be added or removed in the config file. device works fine if connect usb.