I actually discovered the problem.... the coil was fine but in the process of removing the PCB to replace the battery a small component had fallen off the board near the plastic retaining lug that hold the board in... I suspected something was up by looking at the appearance of the tiny pads... Anyway I made a huge guess and decided it was a diode that is missing somewhere around my house and had a go at replacing it with a SOD-323 Shottky I had in parts, slightly too big... but it fits and now it charges!
It works!
Moral of that story.... be very careful hinging out the PCB!