I'm going finally going for a Watch, but I really wonder what will be the version with more battery life : 38 or 42 mm ? Is it really true the equation "bigger device" = "longer lasting battery" as it is for iPhone and iPhone Plus ? I'm also concerned about choosing Series 1 or 2 : gps and waterproofing is not really that important for me, plus I fear that the better screen and the gps can drain too much power, even if the battery is slightly bigger in series 2 ... the fact that Apple states "up to 18 hours" for both sizes and series isn't helping at all ! Any advice ?