Sometimes when I start up the Niro it is competely silent -no engine noise? Other times there is an engine noise -why the difference??

Normally there will be no noise on start up UNLESS you are using electric power for say the headlights....then the gas engine will kick in to essentially add more electric power for what is needed.

Thanks - however, I believe the battery for the hybrid engine is separate to the battery for headlights etc? So, this explanation does not make sense? The hybrid engine battery will not lose power becasue of the use of headlights, etc>?l

The car emits an engine "noise" through speakers located under the hood to alert pedestrians nearby. Without the artificial noise the engine makes no sound in EV mode below 20mph.

Sorry for the late answer. There are a few conditions when the gas (or petrol if you prefer) engine starts when you turn on the ignition. 1. The charge of the hybrid battery is low. Usually this is not the case since there's no way to force EV mode on the Niro and thus the battery operates mainly between 30-70% charge. 2. The charge of the 12V battery is low. Unlike the Hyundai sister model Ioniq, the 12V battery in Niro is charged by a generator attached to the engine. 2. The ambient temperature is low, and the engine needs to heat up to reach optimal operating temperature.

The niro Kia plug in battery won't charge. The car has no electricity. It is dead.