Batteries

Considering that a LiFePO4 battery can last 10+ years, and can be drained below 50% without damaging it plus other advantages such as weight savings, the cost isn't as steep as you think. Yes, the battery costs more than the typical Pb-acid battery, but over the lifetime, you will likely need to replace the Pb-acid battery/batteries multiple times while you would still be using the LiFePO4 battery. LiFePO4 batteries also charge quicker. They don't need a float charge and the have a very slow self-discharge rate. 

The expenses other than the battery are the converter upgrade (if needed), and a DC to DC charger since your tow vehicle likely won't charge the battery as you are driving. This is because the newer "smart" alternator control circuits think the TV battery is charged and reduce the output to save gas. The trailer battery supplies what the TV needs so you arrive with the trailer battery partly discharged. I set up a separate charge circuit with a battery isolation solenoid for the TV that can feed a circuit connected to the DC to DC charger which then charges the LiFePO4 battery. The Grey Wolf came with solar, but it has a cheap PWM charge controller. I purchased a Renogy MPPT controller which will let me connect the TV power in addition to the solar panels. That means that I won't need the Renogy 20A DC to DC charger that I had been using in the RPod either. The last thing you would want would be useful even if you stayed with Pb-acid batteries. That is a way to monitor state of charge. The one I have mounts a shunt through which the negative terminal is connected. It drives a meter that shows voltage, amps in/out, and percentage of charge. It is much better than the "idiot" light gauge that was in the RPod. There is some wiring that will be needed, both for the TV and the trailer if you were to duplicate what I did. However, you may be able to skip the TV part and use the power from the 7-way if your TV cuts that power when the engine is off. You could disconnect the wire from the 7-way on the trailer end and connect up a wire to a DC to DC charger instead. You can't just connect the DC to DC charger into the trailer's existing wiring for supply because then it would be like trying to use the battery power to charge the battery. It just doesn't work.

I detailed the installation in my mods. I removed that equipment and the only things I will be using for the Grey Wolf are the 200 AH LiFePO4 battery and the monitor.

Anyway, I hope that is helpful.

Going through battery expense so far after 12 years, I cannot justify the cost of lithium when looking at what has been spent so far with the old LA batteries, especially when looking at the expense of producing lithium and at the limited rare earth minerals needed to produce them.

3/2011  purchased 2 12v Interstate batteries (deep cycle) @ $ 50 each   total $ 100

8/2020 retired 1 original of the above and replaced with

           Trojan T-1275 which gives 165 AH (incl. core exchange)               total  $ 210

Grand total spent after 12 years service ($ 310.00) which figures out to a yearly expense after 12 years of $ 25.83/year.   I suppose I could add a gallon of distilled water but seeing that it came from my de-humidifier, cost on that was about nil, except for the electricity needed to pull it out of my damp basement. Also didn't include the yearly twice a year cost when they are given a 24 hour 2 amp trickle charge just before storing for winter.