I live in the US and the only way i can buy a battery for my fairphone4 only as a part of the phone, if you have a used fairphone4 or nonworking fairphone but with a workjng battery please put on ebay i will buy it.
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Perhaps you’ve got better chances if you post this directly in the Fairphone forum as well.
https://forum.fairphone.com/
Maybe one of the forum members is traveling to the US on the next couple of weeks or summer. It’s easy to pack a battery in your hand luggage or suitcase (and not forbidden) and then post / mail it to you within the US.