A battery of that size will typically have a capacity of ~500mAh to 1000mAh. If we assume 500mAh then a safe standard charging current would be, say, 40-50mA. It is likely, therefore, that the charger is rated for that sort of current. Your trimmer motor, however, will almost certainly draw a lot more than 50mA, particularly at start-up. Accordingly it is unlikely that the charger will power the motor (as Steve said).