Volt Meter

I'm not new to dry camping so I know the batt will not recharge while making a pot of coffee. I would like to know after running the furnace all night where I'm at. ie Am I @ 12v or 10 or 11 and so on. Wouldn't be 10 LOL the sail switch stops @ 10.5. I have been doing it for over 15 yrs without any V meter. Don't want an expensive control panel just something simple. If I really want to know the exact soc I will check with a hydrometer. Just wanting to get an idea of what I can do before recharging. Thanks everyone for the replies. I'm gonna figure out what I need for my purpose. Just didn't know where to get these things as Radio Shack doesn't have them. The only momentary switch they have is a push button and I want a rocker and they have no panel meters.