Battery charging current is 6A. Circuit draws 3A. Charger has to supply both loads. Charger should be able to supply 9A at 14.5V continuiosly. When battery is charged,it goes into trickle charge stage (by loweing its voltage to 13.6V and voltage stay there). The cut-off circuit is not good in this situation. Current to the battery is monitored and this control charger to adjust charging to maximum 6A. The current to circuit is not supplied from battery terminal but before the point in the chrging lead, where sensor is attached. In this way it does not affect chraging current with load change and charger adjust itself so that it supply current to circuit as required.