MacBook random shutdowns when not connected to power after SMC reset

My macbook pro 13” retina late 2015 shuts down randomly since yesterday. First time battery was at 50% and could only be revived when attaching the computer to power and then turning it on. Now it also shuts down randomly at 80%. The computer has not yet shut down randomly when attached to power and does not shut down immediately after disconnecting the power cord. It seems he keeps working till 80% and then shuts down. As this all pointed towards battery problem i have tried to reset the SMC already two times but it does not work.

Cycle count = 850

Status battery according to apple = normal

With coconut: status battery = good, but design capacity is only 40%.

What can I do? Should the battery definitely be replaced?

Is there a possibility the whole pc will crash and not be able to be rebooted even with power connected?

Any tips are welcome as I really need my computer the coming days !

THANKS