Newbie Battery Question

[Pullin' Chocks]

We are official newbies now having taken delivery of our new horizons majestic 5th wheel earlier this week. We are enroute back to the east coast and now have a better idea of what questions we have. The battery electrical charging system for the most part has us baffled.

We have four, six-volt batteries wired for a 12 volt system. After all day charging with converter and solar, the battery voltage reads 12.6 or 12.7 volts, which seems correct and full based on our understanding of what we have read.

Last night was below freezing and we ran our two propane furnaces set at 60°. We think we used very little other electricity only a few LED lights and a little water through the waterpump and that was about it. When we got up in the morning the batteries were reading 12.1 volts, but that was with a furnace running. The voltage did rise back to 12.3 V after the furnace stopped.

We think the batteries should not be discharged below 12.4 volts or about 50% capacity. Is this correct?

Is it normal for the batteries to drop significantly in voltage when certain systems are running? Should we only evaluate battery capacity with nothing running?

We feel like we are a long way from understanding the battery electrical system even though we have been reading for months. The inverter controls and the solar charger set ups and controls are still to be learned.

Thank you in advance for any information, insight or suggestions that you all may be able to offer.

[SmokeyWren]

I don't claim to know anything about batteries, but here's my experience.

I have an old John Deere diesel-powered backhoe that had two huge 6-volt batteries wired to produce 12 volts for the starter. No matter what I tried, I could not get those batteries fully charged using a good 12-volt automatic battery charger.

So I bought a good 6-volt 6-amp automatic microprocessor controlled battery charger and charged the batteries one at a time. That worked. My battery charger is an Interacter LS series 6-volt 6-amp. Not cheap, but works really good.

Link: Interacter Battery Chargers - Lineage Series - LS - Specs

The picture in that link is of a 12-volt charger, but the specs include my 6-volt model.

Here's one source:
Lineage 6 Volt 6 Amp

But even with fully-charged batteries, I still didn't like the performance of those 6-volt batteries. So the next time I had to replace one, I replaced both with two huge 12-volt batteries wired to provide 12-volt power. Life is much better now, not having to mess with those 6-volt batteries.

[87Rockwood]

It does sound normal but here are a few questions. How long do you wait after removing the charger to the batteries before you measure the voltage? A few (3) hours is a good answer. Too soon and you will get a false high reading due to "surface charge". How much does your two furnaces draw? What 6 volt batteries are you using? True deep cycle? And yes you will load up the batteries a few tenths of a volt while the furnace is running.

[Mr_D]

Yes, it's normal. We have basically the same set up in our MH. Overnight our batteries go from fully charged to 10.9 to 11.0 volts. But we run the furnace if necessary, the TV, or two, the satellite receiver, the U-line ice maker, the 100# storage bay freezer, my CPAP, the43 refer and lights as needed (all incandescent). I just run the generator three times a day for about 2 hours each day when boondocking.

[Pullin' Chocks]

Thank you everyone, We are feeling more normal and comfortable now learning from your experience with 6volt batteries. Our initial idea is to use these 6 V batteries as our learning batteries; In a year or two after we start to move around and hopefully Boonedock more we thought we would upgrade our batteries to 12 V AGM's and possibly add another battery or two.
In attempt to answer the questions, here is what we think:
We have been looking at our batteries as soon as we get into the coach and throughout the time we are inside we'll monitor regularly and also make note when we rise in the morning. We are probably looking way too much but we are on the learning curve. We will have to verify the furnace draw but I believe it is in the neighborhood of 7 to 10 A per furnace. These are your standard fifth wheel propane furnaces we believe. Our batteries I believe are Trojan T105, 4ea. We sincerely appreciate your willingness to help, thank you!

[EngineerMike]

1) Those Trojans are nice batteries
2) you seem to have lucked, or been set up into a good battery balance for your rig & lifestyle. 12.3 resting after running furnace all night should work very well. Many folks run down below 12V, as you can see from D's post.
3) Trojans should last a fair while. If your charger is a single stage they won't last as long and will boil much more causing mess & maintenance issues. Single stage trailer chargers can be upgraded easily and w/out too much expense to a 3-stage charger, usually as a "drop-in" swap. Your owner's manual stack should have the charger specs, if not your dealer can send you to the correct website to get them.
4) when you upgrade to AGMs, there is nothing wrong w/6V size which are fairly common. 12V AGMs are more rare. Although Optima 12V's last fairly well once you trade in the bad one(s) to get a good one, they are also quite small. Size matters, so you don't want to waste footprint for a low volume density battery. The common 6V AGMs have high amp-hours per cubic foot & per foot-print-sq.ft., i'd recommend 6V's. And if you keep your cables from getting corroded you can reuse the ones you have.

["007"]

Here something to add about your RV power systems.
Plus another that may be of interest.

[Half Dimes]

If I did my math right, you have about a 450 amp 12v battery bank. That size is capable of accepting a battery charging output of up to 112 amps (25% of total amp hours). Your charger/converter or inverter should be capable of outputting 100 amps to most effectively charge that setup. Less output is ok, it will just take longer to bring the batteries back to full strength.

I know there is a lot of good info available on the Internet, but I really like a book I bought a few years ago called Managing 12 Volts by Harold Barre. It's very concise and always at hand when I need information.

[Pullin' Chocks]

Great stuff! Thank you good folks.
Your thoughts and experience are a tremendous help.

[Jack Mayer]

What you are experiencing is normal behavior - as others have said. As you gain more experience you will learn the behavior of your batteries better. Furnaces draw a lot of power, over time. When boondocking they are the biggest users of power in many coaches. If you intend to boondock much then I would put in a good battery monitor that show you cummulative amphours of use. It is kind of like a digital fuel gauge, as you use power the counter goes down; as you restore power the counter goes up. I like the Trimetric. New Horizons can install it for you on a service visit - or, if you are handy you can put it in yourself.

[Kro1957]

Originally Posted by Pullin' Chocks

Great stuff! Thank you good folks.
Your thoughts and experience are a tremendous help.

Agreed! Good information!
I run two paralleled 12v in my rig. Have not purchased any solor yet. We did buy a nice generator a few years ago and have never installed or used it yet. Perhaps on our next rig.

[Pullin' Chocks]

We have a battery update. I spoke with Ken at NH ... and probably will again soon. Since the specific gravity was way down on the one battery (of four), even after an equalization; Ken suggested we remove that battery and take it to our battery dealer and have it load tested. If it was bad he will replace it. We appreciated that.
While assessing how that battery would come out I found: that battery date stamped in Dec 2010, the other 3 batteries are date stamped May 2012. So that battery started off with a disadvantage. Then I discovered that the ground nut on the suspect battery was loose. That connection was the final battery ground connection before the cable went out to the coach ground path. I tightened that nut and checked the rest of the connections. They all looked very neat and clean and that one nut was the only loose connection. Right away the battery bank performance improved and became more of what I had expected. We think it still isn't holding quite as good a charge as it should, but it is a significant improvement. We plan to take another set of specific gravity (SG) readings. We will possibly try one more equalize cycle if the SG readings are still off. If the SG readings still are not what we expect for a healthy battery we will proceed with Ken's suggestion to remove and get a load test. I am trying to avoid taking the battery out, it looks like a day long job. (I move kind of slow, but I do move)
Thanks much for all the assistance and support. We really appreciate that part!