Batteries/charger

Plenty of room for 2 Costco 6v golf cart batteries.  I also keep 4 wheel chocks in there along with a quart of battery water and the hydrometer.  I'm going to try to resist putting in more, but there is still a little room.  Here's what it looks like mounted on the tongue: 

I added a battery cutoff switch that I bolted to the forward wall of the box and I secured the batteries using eyebolt secured in the aft wall and heavy rubber shock cords.  I cut the old plastic battery boxes to make trays to hold each battery.  Absent a trailer rollover, the batteries ain't gonna move.  And if there is a rollover, who cares, that'll be the least of my problems.

Trojan states this on the web site:

Visual inspection alone is not sufficient to determine the overall health of the battery.

Both open-circuit voltage and specific gravity readings can give a good indication of the battery’s charge level, age, and health. Routine voltage and gravity checks will not only show the state of charge but also help spot signs of improper care, such as undercharging and over-watering, and possibly even locate a bad or weak battery. The following steps outline how to properly perform routine voltage and specific gravity testing on batteries.

Below that are instructions on how to do specific gravity readings and how to do open circuit voltage checks. Plus it has instructions on how to water flooded cell batteries and how to clean them. All in all, a very useful web page.

Thanks for the info!  I see you have a WDH.  Is that an Equalizer?  That is what I have and I wasn’t sure if I could fit the box but clearly you did.  We have have a 179 and I have about 11.5 inches from the back of the propane to the trailer.  Is that about what you have?

All true and a fine way to go for battery maintenance purposes. With three caveats:

You need to know the specific gravity (sg) of your particular battery at full charge and discharged. Different manufacturers use electrolytes with different mix ratios of sulfuric acid to water, depending on the intended application of the battery. So sg on a fully charged lead acid battery can be between 1.26 and 1.30. Also, some battery designs are "plate starved" and others are "electrolyte starved", meaning that some run out of plate capacity first on discharge and others run out of acid. So you need to know the relationship between sg and SOC for your particular battery. Some manufactures provide data for this, some you'll have to work out for yourself the first time and make your own table. Trojan is really good at providing this data. Also, if you want to be accurate then there is a temperature correction to do to your sg measurements. 

For voltage to work as a measure of SOC you have to measure it while the battery is at open circuit (Voc), meaning no charging or discharging can be occurring. And, you can't just stop taking current or or running current in, you have to wait awhile for the battery cells to reach equilibrium. Typically this takes around an hour or so. 

As with sg, you also have to know the Voc of the battery at different states of charge. This. like sg, varies based on the way the battery is designed. Generally the manufacturer will provide a table or graph for this, but sometimes you'll need to create this the first time like with sg. 

The above caveats are why these sg and Voc based readings are good for maintenance purposes. They take  quite a bit of time to do and you have to take your batteries off line to do it.

If OTOH you want an easy way to see the current SOC of your battery at a glance (the equivalent of  little lights except actually accurate) then get a SOC meter. Much more convenient and they're really cheap now.