A fairly common problem with that particular charger,(Toptron) after the leisure batteries have been renewed.
The charger, more often than not, needs to be calibrated to suit the new battery / batteries.
It is a simple matter of adjusting one of the two or three, I can’t remember without looking again, pcb mounted potentiometers with a flat blade precision screwdriver, a two minute operation, after removal of the offside seat and charger cover of course.
THE MAINS NEEDS TO BE ON DURING THIS OPERATION SO THERE IS A DANGER TO LIFE PRESENT.
The problem with the current situation is that the engine battery is not getting charged whilst on hookup, green light ON.
The charger initially charges the leisure battery / batteries. When the leisure battery is saturated, the charger then shares its output with the load(s), leisure battery and engine battery, green light ON. Without adjustment, the charger will not get to that last stage of the cycle. This is a ‘one shot’ cycle that occurs every time the mains is removed and restored.
If you could make it to Prestatyn in April then I can show you the adjustment but it is wise for the charger to have been plugged in for some 24 hours so that it can be assumed and confirmed by measurement, to be at the end of the cycle.