The solar panel was wired up wrong - basically I wired it up following the colour codes on the wires they provided, despite thinking that was wrong, saw no charge and thought it was the lack of sun. Just for grins, I reversed the wiring (making it correct) and saw a fault, so I made it wrong again. When, in daylight, I reversed the wiring (making it correct again), the battery started charging. Yay, go me. So, it took my spare plane battery (12Ah) from 11.99v to 13V through the day, just leaning on a chair on the patio, so I'm calling that a success.