Lithium-ion batteries degrade even when not in use. A battery that has sat at 0% charge for a decade may be "chemically dead," meaning it won't hold a charge or could even expand and damage the internal components the moment you plug it in.
The iPhone 6 was discontinued by Apple in 2016. Any unit advertised as "brand new" today has likely been sitting in a box for nearly 10 years. This leads to two major issues: buy brand new iphone 6
Most "new" iPhone 6 units on sites like eBay or third-party marketplaces are actually "remanufactured." This means they use an old motherboard inside a cheap, third-party shell with a non-original screen. They look new, but they aren't factory-original. 2. The Software Wall Lithium-ion batteries degrade even when not in use