Welcome to ECF, wheto69. One of the batterie is probably dead or dying. It might be the charger part of the circuitry, either also or instead. Do you use the charger in the device, or do you use an external charger? If the unit is still under warranty, and you use the charging ability of the device, return it. I think that it will probably give that error if only one of the batteries is sketchy, but you could test it by replacing the batteries with known good ones.
edit: and I forgot to mention the dirty batt. contact thing that Storm52 suggested, and if you use the devices' internal charger the issue could be with a dirty or loose USB connection.