Apple has spoken about the issue of iPhone battery draining after updating to iOS 15.4. Apple said, it's natural, really.
This statement was made by Apple via the @AppleSupport account, which replied to a tweet from a user named @jawadaq, who complained about the draining of the iPhone battery after updating to iOS 15.4.
According to Apple, this is normal because apps and features need to adapt to the update.
"Thank you for contacting us. We're happy to help. This is normal for apps and features that need to adjust up to 48 hours after an update. Please send a DM if this problem persists afterward so we can provide further assistance," Apple wrote via account @ Apple Support.
Apple also posted a link to their battery support page, entitled "Maximizing Battery Life and Lifespan". But ironically, one of the suggestions on the page is to update the operating system to a new version, which -- in the case of iOS 15.4 -- actually reduces iPhone battery life.
But the other suggestions on the page are quite useful. For example, avoid charging the battery in a room with a high temperature. According to Apple, the device is designed to operate optimally in room temperatures of 16 degrees to 22 degrees Celsius, and users should avoid temperatures above 35 degrees Celsius, which can permanently damage battery capacity.
Then Apple also advises users to charge the iPhone battery to half of its capacity if you want to store the iPhone for a long time. Also store it in a place that is not humid with a temperature below 32 degrees Celsius.
After six months, users also need to charge their iPhone to 50% if they want to save it again.