Speed has nothing to do with it Colin ..tour mode has always been my " default" setting ..and having previously ridden that route with juice left in the tank ..it was more to do with the conditions of the day ..windy/ freezing cold and muddy..
I wasn't alone in having battery concerns as both Phil and Steve conserved what they had left by switching off completely when mine went suddenly ( the last bar for the first time ever gave very little range at all ) except on the steepest of climbs ..and finished with very little left in the tank .
I'm usually spot on in terms of estimating " range" and have done longer rides with more height gain than this without having to resort to eco ..and it not like I'm using emtb or turbo ...but a 34 mile ride with 3400ft of climbing is pretty close to maximum range even on a warm day .
@RsGaz ..if you felt the weight of my back pack you would maybe understand why carrying a second battery is a complete non starter....
But thank you both for your suggestions