The Xiaomi Redmi Note 9 is a mid-range smartphone by Xiaomi released April 2020. It has a 6.53" IPS LCD display, a 48 MP main camera, a rear-mounted fingerprint sensor, a 5020 mAh battery, and runs on a MediaTek Helio G85.
Well I will Suggest you to checking for software updates, clearing the phone's cache, and ensuring there are no power-intensive apps running in the background. For more check out the following video it might help you in fixing the issue.
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