I'm having the exact opposite problem with two of my three watches (haven't tested my Space Black one yet). Both my S2 Stainless Steel and my S0 Stainless Steel's battery life has TANKED. I don't know if it's an app issue, or what...but I was down to 11% by the end of the day yesterday (usually at about 67%) and then my S0, which is what I wear overnight, I normally wake up with at least 70% battery and this morning it was down to 15%.
Tonight I guess I will spend resetting and re-pairing.
Wow unless you ran 20 km without your phone while playing music with bluetooth that sounds crazy