Why is my inverter/charger displaying error code E12?

Why does my inverter read E12?

An E12 error indicates a worn/bad battery. This is confirmed if the voltage does not rise above 5 volts DC after 1 minute or 10 volts DC after 15 minutes. Check the battery connection are secure and the battery case is intact. Check that the external DC load current consumption is below the charging current setting. Disconnect the DC load or increase the charger current setting. If problem persists, contact Newcastle tech support. http://www.newcastlesys.com/submit-trouble-ticket