Diagnostically speaking I would want to try two things.
# Plug into a computer to see if it is recognized although, at this stage I doubt it, it's still worth a try.
# I would want to know exactly what sort of energy is going through the charge port. If you're actually invested, you can get a [link|https://www.amazon.com/dp/B07GQLYMR9/ref=emc_bcc_2_i|USB-C meter|new_window=true] to tell you more about the power being consumed (or not) by the device. No power going through the charge port could mean a faulty port or battery, but even how much current and what voltages might tell you more.
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***UPDATE***: If you want to check the voltage actually coming out of the battery, the most reliable way to do it would be to test the battery directly. This is a screenshot of an iFixit replacement, so no test points like your pic of the OEM battery. Red pad here is positive and blue pad is ground. [br]
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Here are the spots on the board that PPBATT_VCC (the line for battery power) travels after it gets to the board. You can use any ground point on the board to test against, The long gold strip along the edge of the board here is a ground pad. Anything in red in this picture is on the correct electrical line to test, but I would go for C8593 since it's bigger, and easier to test on. [br]
Diagnostically speaking I would want to try two things.
# Plug into a computer to see if it is recognized although, at this stage I doubt it, it's still worth a try.
# I would want to know exactly what sort of energy is going through the charge port. If you're actually invested, you can get a [link|https://www.amazon.com/dp/B07GQLYMR9/ref=emc_bcc_2_i|USB-C meter|new_window=true] to tell you more about the power being consumed (or not) by the device. No power going through the charge port could mean a faulty port or battery, but even how much current and what voltages might tell you more.