Battery no voltage at flex contacts, but voltage at battery terminals

Hi guys, I have an iPhone 6 plus battery that isn't charging. It has been sitting discharged a long time. I'm trying to manually bring up the voltage a bit so the iPhone will accept it and charge it.

The very tiny battery connector contacts at the end of the battery's flex cable show no voltage with multimeter.

I peeled back the top of the battery to measure directly from the cathode and anode terminals, bypassing the flex cable and its circuitry, and that does show voltage.

These pictures show the area.

I noticed that the positive contact on the flex connector seems to show the correct voltage if the negative probe of the multimeter is placed directly on the battery's negative, rather than on the flex negative. Placing both probes on the positive and negative flex contacts shows no voltage. It would seem the battery itself is fine, but the negative contact on the connector at the end of the flex cable is broken, while the positive contact on the connector seems ok. Unless something else is going on?

Is there any way to fix this, or other ideas? I am trying to salvage the battery. Any help is appreciated.