So which one should it be?

Whatever is reported to iPhones. It's not an excuse to block non Apple devices from reading battery level

All three get reported to iphones.

That’s not part of the Bluetooth spec to report battery power for three separate batteries on one device. Where would it be reported to?

Yes, that's my point.

If it’s not part of the BT spec - how is Apple going to report three battery levels in a way that’s compatible with non Apple devices?