Wireless QI and NFC.
Once I have put everything together with the new battery in place, I have as last replaced the plastic back cover, snapping all the clips back around the edges of the phone. Alas, I was quick to realise the QI Wireless charging has ceased to work.
I almost blamed the battery, or worse, me.
QUICK TIP: there is actually another clip in the middle of the plastic back cover - just press with your thumb just above the 'S' in NEXUS emblem and, voila! Snaps back in.
Wireless charge and NFC - works, once again.