apple watch battery dying every half hour

Hello,

my apple watch seems to have battery issues. when being worn (and having 100%) the battery dies in circa 30 minutes, after that the AW shows online the "charge me" sign on the display. After keeping on the charger it works a while and than all over again.

any idea on how to fix it? is it possible for it to be sotware issue or is the battery dead?

also the AW are series 2 42mm steel case

Thanks.