How do you charge a vehicle with an Exide 10900 Charger Multi-use Power light does not come on but Charging light does - not sure if that means it is working. Plug into elec circuit at same time?

I have found the Exide Model 10900 battery charger to be a nuisance when connected to a slightly discharged battery. Open connection voltage ~ 12.4 volts. The charger refuses light the Charging LED and will not operate. The only way to get the charger to enable is to either connect another charger or battery momentarily so that it senses some higher voltage I presume in order to help it enable itself to charging mode. This must be some safety feature that has gone out of calibration I suspect. Manual mode chargers would not have this problem.