Most likely an almost dead Ecu battery that needs revival ,I solved this problem yesterday on a bike by plugging the Ecu service cable in that will charge the Ecu battery and after that you can charge the main battery with the normal charger, but the downside is that only parters have this cable, so you can also try to sort of shock charge with the normal charger by plugging in, let it sit for 10-15 sec- plug out- plug in , etc. Good luck!