Saturday, April 1, 2023


My RV’s 6-volt FLA batteries are dry, but service manager says they should be good

Dear Dave,
In the fall I purchased a slightly used one-year-old motorhome from a dealer. The original owners made one 350-mile trip in it, decided it was too much for them, and parked it for a year before trading it in on something smaller. Knowing the RV had sat unused for a year, I insisted all batteries be checked (one 12V engine battery and six 6V house batteries). I also had a 340-amp solar system installed and wired to charge the batteries even with the battery disconnect off. The dealer said they confirmed the batteries were good.

I made one short trip and put the RV in storage for the winter. Recently I checked the batteries and discovered two of the 6V batteries were low on water and four were dry … the plates were fully exposed. The batteries have been disconnected via the disconnect switch while in storage, so, I assume, unless the solar system boiled them, they should not be dry and were likely dry when the coach was delivered to me.

I added distilled water and informed the service manager the batteries needed to be checked again.

Reply from service manager

He wrote to me: “There’s really no way to connect a small solar system so wrong that it would damage the batteries: It would either charge when exposed to the sun or it would not. As far as the condition, we can charge them and perform a hydrometer test. If they pass, no further action would be necessary. If they do not, then the sales department would determine our course of action.”

Is the hydrometer test adequate? Are there other tests that should be performed? I don’t want to discover I have bad batteries when I’m boondocking in the desert.

Thank you, and sorry for the long message. —Jim, 2021 Newmar Bay Star Sport

Dear Jim,
Most likely your batteries were Trojan Flooded Lead Acid (FLA) 6-volt batteries that were connected by two in series, which is positive to negative, to create a 12-volt bank, then those three banks connected parallel to create three 12-volt banks. This would provide three times the amp hours, which is most likely 110 amp hours per battery bank, therefore, 330 amp hours. Since they are FLA you can only effectively use 50%, so that means 165 amp hours.

Solar charger would not overcharge the battery with charge controller

I agree with the service manager in his statement that the solar charger would not overcharge the battery if you had a charge controller, which most 340-watt systems would. This would provide a multi-stage charge. If the batteries are fully charged, they would just sit at a float or maintenance charge of 13.2 volts, which is where a fully charged 12-volt battery would not accept a charge.

I would ask the service manager how they initially checked the batteries during the pre-delivery inspection (PDI) and did they verify the cells were at a correct fluid level? If you took one short trip and put the unit in storage, my guess is the cells were not checked and came to you low. However, all owners of FLA batteries must check the fluid level before every trip. They should also check the level and have them fully charged before putting them into storage. Not to throw blame around, but this is common with FLA batteries. We have become accustomed to not looking at batteries because our engine batteries are all sealed and require no maintenance. So, out of sight, out of mind.

A downside of 6-volt batteries

Newmar and several other companies use the 6-volt batteries in series as they tend to have more “cycles” with more plates and last longer so they can power the energy hogs such as residential refrigerators. The downside of them is they gas heavily when being recharged, especially if you have a multi-stage charger such as your solar panels or an inverter/charger, which I’m sure your rig has! Sulfur attacks the plates of FLA batteries as they drain down and the initial bulk charge of a multi-stage charger is high voltage, sometimes as high as 16 volts to break up the sulfation. This causes the gassing and also a loss of the electrolyte. So they are higher maintenance and the fluid level needs to be checked much more often, as you have found.

Several battery water systems available

There are several battery water systems that now make it easier to “top off” FLA batteries with distilled water, such as this system from U.S. Battery. A check valve replaces the original cap and they are all connected with tubing. Before you leave for a trip, insert the supply tube in a gallon of distilled water and squeeze the bulb and all the cells are topped off and not overfilled. This would be the system for your six 6-volt batteries, as each would have three cells.

So, back to the condition of your existing batteries. A hydrometer only measures the individual cells for specific gravity of fluid and can tell you if the cell is good or not. It does not tell the condition of the battery and the level of sulfation. I have discussed this with Trojan, US Battery, Lifeline, and several others as I get the comment “They checked my batteries and told me they were good” all the time. The only way to check a battery condition is to properly charge it, let it sit for a specified time, then connect it to an amp draw machine and count the actual hours before it gets to 50%, which nobody does. So, the service manager will not be able to tell the condition of your batteries with his hydrometer test.

Go dry camping to test batteries

About the only way you can tell how long your batteries will last while boondocking is the old-fashioned way: Go dry camping and see how long the batteries last.

However, there are several variables in this simple method as you need to understand what will be drawing power while you are counting the hours. If you have a residential refrigerator, it will draw quite an amount of power and will vary with different ambient temperatures. The furnace will draw a heavy load as it runs the fan motor. It’s not a perfect science.

However, if you go to and use their calculator, it gets you to start thinking about what appliances and 12-volt components you will be using, how often, and for how long, and should be able to tell if your batteries are performing efficiently. I would suggest shutting off the solar charging system for a weekend test before going out to the desert. Then look at their calculator to see if the 340-watt panels are enough for your battery system and the amount of time you want to camp. I think you might be on the short side.

This will give you real-world test results to go back to your service center.

 You might also enjoy this from Dave 

Can solar panels charge batteries in storage with disconnect applied?

Dear Dave,
My Riverstone has four six-volt batteries with one 100-watt solar panel on the roof. For the past three years, I had access to store our rig indoors with access to 110 v electricity to keep the batteries charged with a trickle charger. When doing this, I switched the main battery switch to “off” to avoid any battery drain. Now, unfortunately, I no longer have access to inside storage with electricity, so I must store my rig outside and depend on the 100-watt solar panel for keeping the four batteries charged.

My question is: When I turn the main battery switch to “off” to prevent battery drain, will the solar panel still act as a trickle charger to keep the batteries charged while in storage?

Read the rest of Greg’s question and Dave’s answer.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

Read more from Dave here


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15 days ago

I’m the Jim who wrote the question. Excellent response from Dave and good feedback from readers. The real moral of this story, don’t assume the service center followed through on your needs. You never know to whom they assign a task, especially a simple one. As I told Dave in a separate email, I check PSI every trip and battery fluid frequently. I got lazy and assumed the service folks did their job. My dealer has an excellent service shop. But, like I said, always make your own checks. I didn’t.

Diane McGovern
15 days ago
Reply to  Jim

Thanks for the update and excellent advice, Jim. Have a good night. 😀 –Diane at

15 days ago

Similar to Martyn, below, I had 2 6v Golf Cart batteries in my RV. I checked the water every-few months, and only had to add water once in 4 years. I dry-camped most of the time, and relied on solar panels to charge. Camped in winter (eastern plains of Colorado, so cold nights, and mostly-sunny days).

I went to Oklahoma last summer, and plugged-in to shore power for a couple of weeks. Went on a trip in southern Colorado a few weeks later, and solar panels did not seem to be keeping up. I ran a generator (had never used it before), and still seemed like low voltage. I took the caps off the batteries, and all cells showed no water, but did have moisture on all plates. Ran into town and got distilled water, filled batteries, then the next day drove 5 hours in great sun. Batteries worked as well as they ever had, even over some winter hunting trips.

The golf cart batteries are more robust than 12v. They can be discharged below 50%, and apparently don’t suffer.

Thomas D
15 days ago

Years ago batteries were shipped dry. You added sulfuric acid and gave them a charge. Rather than water, how about using acid instead?

Roger B
15 days ago
Reply to  Thomas D

That would a good question for Ask Dave. From what I recall you should never add acid to an older battery. I remember something about “you can add water to acid but cannot add acid to water”. The acid in used batteries is more like water in this respect. Not sure of all the chemistry. Hopefully someone with better knowledge will respond.

Wallace Wood
16 days ago

As a general rule of thumb, once a FLA battery cell goes dry the battery is no longer any good or has lost a lot of its capacity.
I would fill the battery with distilled water and charge. let the battery sit over night and check each battery with a DVOM. Each battery should read 6.2-6.3 volts. If the battery reads less there is a good chance of a bad cell. Use a hydrometer to test each cell.
The only other quick way of testing the battery is with a load test with a carbon pile which can put a 300-400 amp load on the battery. old school technology but it works well on 6 volt batteries.

Martyn Price
16 days ago

I inadvertently failed to maintain the liquid level on my two 6 volt batteries. They may even have been completely dry or close to. I added distilled water and then started charging. I was resigned to an expensive trip to the battery store.

That was over two years and many camping trips ago. The batteries took charge and have performed well since.

Tommy Molnar
16 days ago

I went to six volt batteries a long time ago (over 20 years ago). Trojan 105s to 125s, and finally to 145s. My last upgrade was to two 100 amp hour lithium batts from Expion. I found there to be some limitations I did not take into account (from ignorance) when switching to the new technology. After some trials and tribulations, I finally got things working as they should. I got lots of help from Expion, Morningstar, and Progressive Dynamics. Life is good now but it took more time than I had anticipated.

Wayne C
16 days ago
Reply to  Tommy Molnar

I also went to 6v batteries about 20 years ago and have since changed to Battle Born lithium batteries. The 6v flooded lead acid (fla) batteries were a great improvement over 12v fla and the switch to lithium was even much better than the 6v fla. I only had to replace the converter/ charger to a lithium compatible unit and change the charging parameters on the solar charger. Some of the benefits over the 6v fla setup are twice the available power, less than half the weight, no outgassing, no water level check, and about half a volt higher operating voltage. The only disadvantage was the initial cost, but if they last as long as advertised, that will even be less over time. I’m done with flooded lead acid batteries for RV use.

Tommy Molnar
16 days ago
Reply to  Wayne C

My lithium battery issues came from unexpected sub-freezing temperatures, and finding out that unlike lead acid batteries, you should not store lithium batteries at 100% charge. Now, if we’re going to be in an RV park for an extended time I disconnect the batteries after dropping them down to between 60 and 70%, I disconnect the batteries from use and just use the onboard converter.

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