First, check if the battery is bloated or not if it is bloated change it with a similar 4500mah battery.
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If the battery is not bloated first change the app's background running setting to off from setting and stop other background processing you don't want. [br]
Next, stop all unnecessary notifications and turn on the dark mode it boosts your phone battery life.[br]
If it didn't work try replacing the battery and check if that resolves the problem.