Same charm on belt

I need help understanding regarding a situation when you put same charms on a belt, how do they act? Are they getting consumed at the same time alltogether or by turns ?

Example :
I have 3 x 18% Chaos resist charms on a belt 80 charges, 40 charges per activation duration 4 seconds

Do they activate one after another, with me getting 18% chaos resistance for 4*80/40*3 = 24 seconds ?
Or they activate alltogether with be ending up having 18*3=54% chaos resistance for 4*80/2= 8 seconds ?

Thank you !

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