Default Weird Battery

Hey All

so the battery is sometimes working good
2.5 hours screen time took 45% battery

and sometimes i charge the battery and the battery doesn't hold a few mins
its shutdown and need to recharge it again

what is the problem the battery or the charging connection ?

it start when i plug it to charger with 30-40%
if its empty and i charge it its wont do this problem

thx for help, sry for the English
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