Why is my ipone xr 0 remaining charge

Your battery's BMS, or Battery Management System - the small circuit board attached to the battery - is responsible for reporting the battery's charge state to the phone's processor, so a failed BMS can cause the kind of issue you're seeing where the phone doesn't get valid charge information from the battery.

Does the phone turn on even with the battery reading 0%? Does it come up when plugged into a charger? I'm going to assume you've eliminated your charger and Lightning cord as the source of the problem before you went any further, right? Because obviously if your charger or cord is bad then your phone isn't going to get charged.

The most likely fix for this would be to replace the battery thus giving you a new BMS that will correctly report the charge information. It is possible for there to be other causes but those would generally be motherboard issues that would take some serious upper level expertise to fix; not something you or I could handle.

So my best suggestion is to replace the battery and re-evaluate if the problem is still there afterwards.

iPhone XR Battery Replacement - iFixit Repair Guide

Be aware that Apple started pairing the battery to the logic board with your phone and the XS, so you will see a couple of effects of that when you replace the battery yourself. First of all, you'll get a pop-up notification for a couple of weeks to the effect that your battery may not be genuine - even if it is. The pop-up will go away after a couple of weeks, but there'll be a notification badge on you Settings icon with the same sort of message found under the battery heading, and that badge will be there permanently.

In addition, Apple will disable your ability to view the battery health percentage, taking away a valuable tool in knowing when it's time to replace the battery.

But other than those two things the battery will charge and work normally. Unfortunately, your phone is too old to be eligible for Apple's Self Repair program, so the only way to avoid the messages and the loss of health information is to pay Apple to replace the battery. There are ways around the issue that involve spot welding and a device programmer, but for most of us it's not worth spending an extra $120 for tools to do a one time job on a $15 battery.

Good luck with your repair; let us know what happens with it!