How to monitor battery state of charge

I would go with the volt meter, and as time permits I'd calibrate it to the state of charge figures from a hydrometer.

In your next week time frame: I'd suggest a "cigarette lighter" plug in voltmeter and a hydrometer both available from Amazon. You might be able to find them locally. O'Reilley Auto Parts used to have a hydrometer for less than $10, and I think I've seen the plug in voltmeter in auto parts stores.

There are very good systems available, but I don't think you have time to investigate and install them now.

2 good GC's should give you a couple of nights run without trouble unless you use a lot of heater fan.

Regards,
Doug

A true battery gauge will involve a shunt to measure the current in and out of the battery. You program the device for the AH of your bank and it will keep track of how many amps have gone in and out over time. This is a far more accurate than a simple volt meter. A battery's voltage fluctuates based on whether it's being charged or discharged when the volt reading is taken.
One simple and fairly inexpensive battery gauge is the TriMetric. They make several different model, the TM-2030-RV would be the one I'd look at. Link10 is another gauge that is worth considering.
If you do plan to ever get a nice inveter/charger most manufacturers also make a battery meter. They typically will plug into the communication bus of the inverter/charger and allow you to see the battery level on the same display keypad. Magnum, Outback, and Xantrex all offer these; I think Victron has one too.
A hydrometer is really the best way to know how your batteries are doing but that can get messy and is best left for occasional check ups at home. A simple volt meter, or worse yet the idiot lights that come with most RVs, is a very simple, inexpensive, and rather inaccurate way of trying to determine battery state of charge.

Leaving next week? Simple voltmeter is fine.

Plan to run the generator for a couple hours starting the second day.
12.4 to 12.0 is time to recharge with increasing urgency as you approach 12.0 volts.

The 12 Volt Side of Life

No way would I take a hydrometer camping.
Not sure how the hygrometer on your weather station will help.

Yes, I'm sure he wants to be messin w/ a nasty hydrometer every day while on a camping trip.

I can tell you an easy fool proof way to monitor, w/o a monitor.
Listen to the water pump,....if you notice a noticeable slow down in pump speed, along w/ noticeable light dimming, it time to charge.

x2 for the Hygrometer for flooded cell...

or current integration (coulumb counting) for any battery type

Get a battery hydrometer.

You can find 4 digit digitwl volt meters at places like ebay reasonable. Thats what I did plus a momentary push button switch and I can see the voltage at a glance.