Over the past few weeks have noticed that engine battery is not fully charging when connected to shore power. It's been sitting at 12.5V while plugged in. When connected the house battery is typically above 13.7V. House batteries have dropped as well (13.2-13.3V). House batteries are brand new and connections tight and clean. Started to think engine batteries are the issue. Looking for date code. Sticker on front shows H6. Does that really mean July 2006?