Why does my inverter display error code E03 with nothing plugged in?

Why does my inverter read E03 with nothing plugged in? It has been working fine until now.

A low battery can sometimes generate a false error. Disconnect the battery terminals for twenty minutes, then plug back in to charge. Then check the datecode and battery voltage. Try replacing the batteries or swapping them with another functioning cart or powerpack. If new batteries do not resolve the issue, the inverter/charger may need to be replaced. If issue persists, contact Newcastle Techical Support. http://www.newcastlesys.com/submit-trouble-ticket