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With any device, if it hasn't been charged in some time, it's possible that the batteries of gone completely flat in which case they would need to be replaced. When a batteries recharge the charger needs to read certain information from it, which it cannot do if there is no voltage in the battery at all. Also, over time all rechargeable batteries eventually need to be replaced. If you have had this device for a while and the batteries have recharged up until now, you may just need to replace the batteries with new rechargeables. If you would like more specific information about the type of batteries to use and where to get them, please let me know along with the model number of your specific device.