Some laptops will display that if you are using an after market charger, or if the charger is not providing adequate power to both run the laptop and charge the battery simultaneously.
I've had bad luck with cheap aftermarket chargers from ebay. I recommend getting a replacement made by the manufacturer if possible. At least make sure that the wattage is correct for your laptop. Check the power specifications on the original charger, or look under the laptop for the power input specifications.