Asking here, since no way to directly ask iFixit (frustrating!)

There's a lot here to unpack!

This replacement battery is what you need to bring that dead smartphone back to life.

• This battery is brand new! Each one has been tested to confirm that there are no cycles on the cell and that the capacity is 95% or higher.

Batteries have Cycle counts so you don't want one that has been used.

iFixit tests the batteries from the factory to make sure it's good.

As to the battery not being 100% batteries age!

Just sitting on a shelf which is why it's hard to find a battery which is smack 100% I've even seen batteries which are over 100% by 8% or lower at 92% because the chemistry has aged in the battery

As to the warning that's Apple for you!

I'm sure you take your car to the Ford dealer so the oil filter and oil are for your Ford or what ever. You don't go to the Jiffy Lube or other independent oil changing shops or do it your self getting the oil and filter from the auto parts shop.

As Apple is unwilling to set a standard for compatibility, 3rd parties are limited to what they have reversed engineered. You can also encounter Apple doing a firmware update which can effect things. That's been less of an issue these days.

Apple only recently offered direct sales of its parts, sadly your XR is not offered you will need to get Apple or one of their authorized service centers to replace the battery, but it will be more expensive. Here's a rundown of Apples policy, they are:

1. Supported - Up to 5 years after the end of production. Full support for both software updates & hardware repairs.
2. Vintage - Between 5-7 years after the end of production. When an Apple device becomes “Vintage” it will no longer receive routine software updates and isn’t guaranteed by Apple to be repairable at an Apple store or authorized service provider.
3. Obsolete - 7+ years after the end of production. Obsolete products lose all support—no more repairs, system updates or security patches.