Lots of good advice from others here, so consider this a ditto on some good comments and a twist on some of these ideas. This is a bit of a book. Bear with me.
I'm a veteran boondocker, and with a 100 watt solar panel and a single group 24, and frugal power consumption, I can go indefinitely without shore power. I have a genny that I use for about 15 minutes in the morning and in the evening to run 120 volt appliances (micro and coffee maker), and during that time I get a tiny bit of charge in the morning, but virtually nothing in the evening, because the solar tops off the battery during the day. The situation you describe does not make sense....it's an indication that something is wrong.
You're boondocking, so as others said, you need a generator or an inverter on your TV (tow vehicle) to supply 120 volts if you plan to use a regular battery charger. Once you get to that point why not just plug your rig into the generator and allow the converter/charger do the job? It's a better charger.
Adding a second charger in parallel (alligator clamps to the battery terminals) is OK. It's no different than jump starting your car, having it start, and having your car's charging system charge the battery simultaneously with the other car thru the jumper cables. In fact, solar works the same way. You just connect the output of the solar charge controller straight to the battery in parallel with the converter/charger.
But, with that said, your converter charger will feed the battery about as quickly as the battery can take it. So there's no real benefit to putting two chargers in parallel. Batteries also self regulate charging...they only accept so much at a time.
Now, what's the problem with your system?
~ Others point to a bad battery. I tend to agree. 2017 is a pretty new rig to have a bad battery, but they do fail, especially if abused. Abused means draining it dead before recharging. Doing this once or twice will cost you a year or more off the life of the battery. Making a regular practice of using too much capacity will kill the battery very quickly.
As someone said, a typical group 24...the "free" battery dealers routinely install...has a capacity of 70 to 80 amp hours (AH). You get to use half. Let's keep it simple and say you get to use 40 AH, then you must recharge.
I'll come back to this later and talk about how you can plan around power consumption. A new battery will perform as it should, and with FRUGAL use of power, you should be able to get a couple of days out of it. But frugal means FRUGAL. You need to understand your loads: lights, furnace, water pump, spark ignition for hot water heater and fridge, exhaust fans, parasitic draws (see below). You CAN'T run the lights like you're in an RV park. Furnaces are power hogs, so use it carefully...not all evening.
Even with solar, we use a propane mantle lantern (heat and light) and LED battery powered lanterns for light. Period. We take the removable faceplate off our stereo to eliminate drain from the LED display. We do NOT use the outside lights...again flashlights and LED lanterns. Since our PUP (former camper) was just a glorified tent, and since we camp in the Rockies at about 8500 feet, it's cold at night. We save the power for the furnace. Our furnace consumed 5 amps when running and on a cold night it ran on about a 50% duty cycle. So to heat the camper for 8 hours, it ran 4 hours, at 5 amps per hour, equaling 20 amp hours all by itself. The other 35 or so was split between all other uses. A water pump doesn't run long but it pulls 7.5 amps minimum. And so on.
A 12 volt group 24 is not a good option unless you have solar. More on that later.
~ Your converter/charger could have gone bad. It happens rarely, but it happens. If your converter isn't charging properly, your battery will end up going dead. But the WFCO brand equipment in your rig is pretty cheap. Don't be alarmed. Replace it and the battery it ruined, and you're good as new.
~ UNLIKELY, BUT you MIGHT have one or several "parasitic" draws on your battery that shouldn't be there. Some must be there. The CO/propane detector is a notorious parasitic draw that you can't live without. But it should only consume about 3 amp hours per day. Others include all those LED panels on the entertainment system, pilot light on the TV, and so on. But, is there something else? Get a multimeter. You need one and they are cheap....$20 for a good one. Set your multimeter to DC AMPS. Disconnect from shore power. Turn off everything that can be switched off in the rig, then disconnect the negative cable on the battery and use the multimeter to "jumper between the black cable and the negative terminal on the battery. The multimeter should show a tiny amount of current. Documentation for your CO/Propane detector will tell you the draw, and you can assume the stereo display might account for .25 amp or less. If you are showing 2 or 3 amps of draw with "everything off", understand that this is 2 or 3 amp hours every hour 24 hours a day. 2 amps would mean 48 amp hours of parasitic draw, which is more than the battery can safely deliver! That means something is on that should not be on. If that's the case, you must hunt it down and find out why it's on.
~ Downright battery abuse is another option...unlikely because you are aware, but I'll mention it. You must regularly top off your battery cells with distilled water. Once the plates are exposed, the battery will be ruined in short order. I check the levels in my battery about every 3 weeks or so.
Buy distilled water and a turkey baster at the supermarket. Fill with distilled water, and use the turkey baster to add the water to the cells.
~ Corrosion: The crud that builds up on battery terminals and cables is insidious. You clean it with wire brushes, a high concentration baking soda/water solution (and clear water to flush) and an old toothbrush to scrub. You prevent it with battery terminal grease or other methods. BUT ONE OF THE MORE INSIDIOUS types of corrosion is in the clamp-on quick connect terminals clamped onto battery cables. If you have one or more terminals that are all crudded up inside the crimp on, you may be wise to clip them off and replace with new ones from the local hardware store. Be sure the new wire end is nice and shiny clean. One bad connection can wreak havoc with both charging and consumption. And unlike your car, when you turn the key and you just get a click, cruddy and bad terminals are quiet about the problems they cause. You must be fastidious in your efforts to keep your electrical connections clean in and around the battery box.
AND THAT INCLUDES ANY GROUND WIRES THAT ARE SCREWED TO THE FRAME. A bad connection at the frame can bugger everything, and in MANY cases, the wiring diagram includes using the frame as part of the wiring circuit.
CHAPTER 2 (sorry, this is a book).
So you wanna boondock? Generators are wonderful for 120 volt power for a few minutes. Generators suck when you need to listen to them all day. As others said, the way charging systems work, "BULK" charging at high amps happens for a brief period, then the WFCO (and other brands) of chargers kick down to a lower rate of charge. The result is that to replace 35 amp hours, you'll need to run the genny for 6 to 8 hours a day. What fun!!
If you're serious about boondocking, you need solar. I mentioned that I got by with a single 100 watt panel and a single group 24. And with that I was able to use an inverter to power a 120 volt electric blanket for 15 minutes to take the chill off our bed. To be clear, a 360 watt electric blanket sucks 30 amps at 12 volts. But 1/4 hour of use meant I was consuming about 8 amp hours...one of the other uses mentioned above. Not using the lights let us warm the bed.
On my new rig, I'm installing a 400 watt Renology solar kit and two 6-volt Trojan golf cart batteries in series. The battery bank has a 225 amp hour capacity, and I get to use about 115 amp hours of that. Almost triple the capacity of my pathetic little group 24. Our new rig has more bells and whistles, including an electric awning, the main slide, and so on. The furnace is bigger. We plan to indulge in using the lights. And we'll still prewarm the bed with the electric blanket. This new system will handle that kind of load.
Windy Nation and Renology are both reliable brands. My Renology kit:
If you don't want the golf cart batteries, you can buy two group 27 12-volts and run them in parallel. That should give you about 80 to 85 amp hours of USABLE capacity...more than double what you have now.
From there, you could add a small inverter for 120 volt power during quiet hours, but, like my use, you must be VERY careful how much you draw thru an inverter, because they absolutely inhale power at staggering rates.
And one more thing. That cute stereo/entertainment system built into your rig sucks power relentlessly. Those pretty LEDs never give up. I'm pulling mine out of the face plate and installing a switch in the power line to ensure it shuts off 100%. 120 volt TVs only have parasitic draws on live outlets, but the trend today is 12 volt TVs. Pull the plug. If you want entertainment, feel free to turn it on and calculate the load. But it shouldn't be draining your battery when you're not using it.
One last thing. How do you know how much power things use? Simple math. Everything in your rig has an owner's manual with power specs. The specs will include either watts or amps for all items - both 12 and 120 volts.
When boondocking, only the 12 volt items count, but they ALL count.
This calculator can help: https://www.rapidtables.com/calc/ele...alculator.html
Current is what matters. Amps...add up to amp hours....the most important number. Convert watts to amps with the calculator...using 12 volts. Always 12 volts, because that's your power source.
If you get an inverter and run a 120 volt appliance thru the inverter, it's still drawing from 12 volts, so always plug 12 volts into the calculator.
Example: my electric blanket is rated at 360 watts. Enter 360 watts and 12 volts and you get 30 amps.
Boondocking is the best camping. To boondock you must start with enough battery and enough charging capacity and then know your loads. And, of course, you equipment must be in working order.