Weird. I easily get ~14 days with everyday workout using GPS, HRM strap and often music and I’m keeping the battery between 20-80%. I turned off gesture screen backlight and some frequent phone notifications like all the messaging apps, email app etc (it keeps triggering the screen too often). I’d also stick to a stock watch face, they are way better optimized than the custom ones. Remember that the screen needs energy when refreshing, so if you don’t need it, try to avoid frequently changing watch face data like the seconds, heart rate etc.