my apple watch just die and wouldn't restart. this happen at least once a week

The watch is not flat, it just shut off. When I put back on charge it turn back on with at least 80% full.

The watch charge fine. It just shut off and can’t be woken unless I put it on charge.

It’s only turn on when on charge. No button on the watch respond. As if it’s dead. However as soon as it in charge it shows the watch at least half full 🤨