On opening the control box up I can see on the main PCB something that looks like a resistor has badly overheated. On removing it the legend on the PCB underneath looks like "l4.7R" but the dot and the R are indistinct. Is it a 14.7 ohm resistor? It might well be in the battery-charging circuit. At present its measured resistance is around 10k but it may well have burned out too much for this to be reliable.
It's about 11 mm long, and instead of colour bands it has an odd spiral pattern: https://photos.app.goo.gl/QUrYiABWSeXHwR947
Thanks in advance for any help.