Just plug all the battery slots in parallel to a 4.1V power source (that's a nearly full battery voltage). You probably have to solder them to make a reliable connection.

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randomblock1 3 hours ago | parent [-]

I'm pretty sure the third/fourth pins are used for communication to the battery. I doubt the phone would be happy it wasn't responding. I vaguely remember some phones can just use a resistor for that pin? Either way it's not quite that simple.

	▲	cowlevel an hour ago \| parent [-]
		Maybe. Try it and see. If it doesn't work it's probably just a temperature sensor (thermistor) and a resistor indeed simulates a certain temperature the same way your power supply simulates a charge state.