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obviously the physical battery size and capacity are different between the 7 and 7 plus, but what about the connector plug? strictly for testing and diagnostic purposes, could i power up a 7 Plus with a 7 battery or vice-versa? Thanks
I would recommend using a battery rated as compatible for a 7+ for testing and diagnostics as it would best represent the end result use-case. Still, it should work to power up an iPhone 7+ with a battery from a 7. They use the same connectors on the battery and motherboard. However, a problem may arise from the (edit: very slight, 0.02V) difference in voltage between the batteries used by the devices and could cause damage to the device and battery, and I would not recommend going the route you are suggesting.
