After replacing the battery (with iFixit kit), the watch was working well for a couple of days. I didn’t drain the battery down under 10% during that period (my bad). The green snake appeared. I let it drain for 2 weeks until nothing appears on the screen (as suggested on many youtube videos). I charged the watch again and it come to life, I was able to use it for a couple of days. This time, I managed to drain the battery under 10% before charging it. The green snake come back! I will check the voltage (as suggested by Amy Halfacre). Is there other suggestions?