Acer 315 Runs Hot While Charging

Got a new Acer Chromebook 315 just before Christmas along with a cooling pad and I've noticed to runs very hot during charging. If I open the Diagnostic panel the internal temp is often around 70C even with the cooling pad in a cool room and usually in the lower 30s when it's running on battery. Is this normal for this model or should I return it and get another one? TIA.