By all means, use the charger. For a lead battery the voltage is important, not the current. It might take a little longer to charge.

Post questions in the Rubber side down section next time.

1.4 is MAX charging current you are at a lil more than half so figure twice the time..but  SLOWER is better cause its a DEEPER charge.. 3/4 amp charger is fine for those who hibernate their bike for the winter, i'd be cautious with lower dollar chargers(not lower amp)that dont have a trickle/maintenance circuit..insure your electolite is up and caps are off in a well ventilated area
the acid mix is explosive!! maintenance free batterys have no caps hence no way to suplement electrolite but ample ventilation is safer..