Error: L6218E: Undefined symbol ble_bas_battery_level_update (referred from main.o) Error: L6218E: Undefined symbol nrf_drv_saadc_buffer_convert (referred from main.o)
Error: L6218E: Undefined symbol ble_bas_battery_level_update (referred from main.o) Error: L6218E: Undefined symbol nrf_drv_saadc_buffer_convert (referred from main.o)
You should not include .c-files the same way as header files. you should add them to you project as I described above. Have you also ensured that SAADC_ENABLED is checked in the sdk_config.h file in the Configuration Wizard? 
You should not include .c-files the same way as header files. you should add them to you project as I described above. Have you also ensured that SAADC_ENABLED is checked in the sdk_config.h file in the Configuration Wizard?
