Question: Can I use external bench supply for VBAT in CYRF6936?
Yes, it is possible to disable the PMU and provide an externally regulated DC supply voltage in the range of 2.4V to 3.6V to the VBAT of the device. If you use an external supply for VBAT, make sure it is of the LINEAR regulator type that can deliver at least 0.5A of current (the switching regulator's inductor has a peak charge current of up to 400 mA). You can disable the PMU through SPI write. Figure 9 of the CYRF6936: WirelessUSB™ LP 2.4 GHz Radio SoC datasheet gives the recommended circuit for using external supply with PMU disabled.