I had the same issue with my new 6940. I had it for about 2 weeks, maybe, and every time I picked up the handset it would say the battery was low even though the light on the handset would indicate it was fully charged. I tried disabling the Bluetooth, rebooting the handset, reconnecting the battery, repairing the handset, and rebooting the phone while the handset was off. Nothing improved it until I had my partner replace it. Since then it's been fine. So might be a bad batch of batteries from the manufacturer.