After updat my iphone XR version 15.2.1 that my phone battery health is going down day by day .how should i do?

Hi kyi62,

We understand you have concerns with your maximum capacity and we're happy to help. We can start by learning more about batteries and the maximum capacity here: iPhone Battery and Performance

As stated in the article above, "As lithium-ion batteries chemically age, the amount of charge they can hold diminishes, resulting in shorter amounts of time before a device needs to be recharged. This can be referred to as the battery’s maximum capacity—the measure of battery capacity relative to when it was new."

Best regards