I haven't found any yet shwoing that a new battery is part of the deal.
If it were me, I would buy directly from Apple. Not only are you guaranteed a new battery with the iPhone, it will also come with a one year AppleCare warranty. Spend a bit more to get a lot more.
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Refurbished iPhone Deals - Apple
IF....a third party company that refurbished the phone was officially approved by Apple, it will come with a new genuine battery. Unfortunately, you will not really know whether the company was officially approved as an Apple refurbisher unless you first buy the phone and check the Model Number.
Otherwise, any shop can call a used phone "refurbished"....and also call themselves iPhone experts.....so you won't know whether the phone was refurbished or used....and you also won't know if the shop used genuine Apple parts in the process. A phone with less than 100% Battery Health is a used phone, no matter what the seller might call it.
Don't buy a used phone. We get multiple posts every day from users who thought they were getting a good deal, and find out too late that the phone has problems.
The All Too Common SAD Reality of Buying … - Apple Community