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Old 12-05-2021, 11:08 AM   #1
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House batteries burning question

Next summer we are planning an extended trip where we will be doing a lot of boon-docking. Now, our house batteries do everything asked of them but they are more than 4 years old, will be 5 by departure time. I talked to Battery Guys about changing them and they advised that it wouldn't be doing new batteries and favor to let them sit for several months before using them and to wait.

My fear of waiting is they won't be available when wanted and also that the price will go up. With that, two weeks ago I installed new batteries. Now, it weighs on my mind that they are not working just like a welfare recipient.

Day before yesterday I decided to do an experiment disconnecting shore power and turning on the inverter. Our inverter has a green, amber and red light to indicate battery charge. Our old batteries didn't like the inverter and in a short period of time the green light would go to amber. Even with no load they didn't like the inverter drain. With the new ones I was surprised that after several hours the inverter light was still green even though the only load was microwave clock and two lights on TV's. So... I decided to leave the inverter on over night. To my surprise in the morning the inverter indicator was still green. Now, after 24 hrs I decided to turn a TV. It took another 45 minutes for the indicator light to turn amber. At that point the shunt was still reading 12.6V.
I plugged shore power back in and at that moment the indicator light turned red. By the time I looked at the shunt the volts were over 14 and we were charging.

So.... for the battery gurus with more experience and knowledge. Is this a good exercise once in a while when the RV is going to sit idle for a few months or is it better just sitting without battery activity?
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Old 12-05-2021, 11:27 AM   #2
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Well those green/amber/red lights are a very poor indicator of state of charge (SOC), at best +/- 20%.

Your old batteries were turning bad and that is why the light changed after a short period. The new batteries had much more real capacity so stayed green longer.

BTW a shunt does not measure voltage, it measures current. The only way to really know how much current and amp hours you are using is to install a shunt based battery monitor that shows amps and amp hours used. In descending order of price check out Victron, Renogy and Qwork- see https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

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Old 12-05-2021, 11:46 AM   #3
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My suggestion.

Fully charge the batteries using shore power, at least overnight. Then, completely disconnect the batteries from the RV by removing the negative cable to chassis. The batteries are now isolated as if they had been removed and are sitting in the store, unpurchased. There will be no difference in the batteries in five months. The're either sitting on the store shelf, or in the "shelf" of your RV.

Leaving the batteries in the RV but "disconnected" via the disconnect switch, does not remove all electrical drain. Further, "exercising" them as you described is putting some strain on their life in that recharge cycles are occurring and you will need to keep adding water to the cells.
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Old 12-06-2021, 02:34 PM   #4
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“So.... for the battery gurus with more experience and knowledge. Is this a good exercise once in a while when the RV is going to sit idle for a few months or is it better just sitting without battery activity?”

Congratulations! Of course, you made the correct choice.

Your procedure is a good one, especially since you fully understand how it works and what the results mean. I say go for it from time to time.

I don’t understand the advice to “sit idle for a few months”. Using that as a test does not reveal much.

There is a lot to learn about managing a battery powered system. I see you have a battery monitoring system that has a shunt. Those are usually good tools. Does yours keep track of charge base on the current? My cheap one does not.

I am not sure what you imply about the 12.6 volts while the inverter and TV are “on”. There are three basic voltage profiles for lead acid batteries. They are Charging, Discharging, and Static or Resting. Resting voltage can be used to estimate state of charge. Discharging voltage is always lower than Resting. Charging voltage is of course always above Resting.

Storing for a few months is of course an important issue. Doing it correctly leads to long useful serviced life. I am not sure what advice you want about it. I will try to attach instructions about storing.
Attached Files
File Type: pdf Storing Lead Acid Batteries.pdf (101.5 KB, 5 views)
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Old 12-06-2021, 02:44 PM   #5
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I believe you did good. Occasionally cycling the batteries to 80% state of charge and then charging back to 100% is better than remaining on float for months with no activity.
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Old 12-06-2021, 02:58 PM   #6
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My storage method is to let the battery discharge when disconned from any load. Then I charge for 24 hours when voltage hits 12.2v. I expect and they do last for 7 to 10 years. Once the load capacity gets down to about 80% I get new battries.
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Old 12-06-2021, 03:57 PM   #7
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Battery maintainers are wonderful things. Some inverter/chargers or onboard chargers have the same kind of tech behind them. The onboard charger in my cabin cruiser has a dual output system and has an AGM mode to support the AGM batteries I installed when I purchased the charger... in 2013, and the batteries are still going strong. This charger will raise the voltage every month for a few minutes to help boil off any sulfation which tries to grow. The converter/charger I have in the Dutch Star does the same type of thing. If you're unsure if your system does this, just purchase an outboard battery maintainer and hook it directly to the batteries once you've disconnected them from the rig. I've had good luck with the Deltran brand battery tenders. A maintainer is a better choice than just leaving them disconnected, which, depending on the battery chemistry, would be a poor choice.
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Old 12-06-2021, 04:11 PM   #8
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Quote:
Originally Posted by Persistent View Post
“So.... for the battery gurus with more experience and knowledge. Is this a good exercise once in a while when the RV is going to sit idle for a few months or is it better just sitting without battery activity?”

Congratulations! Of course, you made the correct choice.

Your procedure is a good one, especially since you fully understand how it works and what the results mean. I say go for it from time to time.

I don’t understand the advice to “sit idle for a few months”. Using that as a test does not reveal much.

There is a lot to learn about managing a battery powered system. I see you have a battery monitoring system that has a shunt. Those are usually good tools. Does yours keep track of charge base on the current? My cheap one does not.

I am not sure what you imply about the 12.6 volts while the inverter and TV are “on”. There are three basic voltage profiles for lead acid batteries. They are Charging, Discharging, and Static or Resting. Resting voltage can be used to estimate state of charge. Discharging voltage is always lower than Resting. Charging voltage is of course always above Resting.

Storing for a few months is of course an important issue. Doing it correctly leads to long useful serviced life. I am not sure what advice you want about it. I will try to attach instructions about storing.
Paul, Thanks for your attachment. I forgot to mention my old and new batteries are AGM. The info you provided inspired me to check my Xantrax inverter/charger setting. Sure enough it was set for wet batteries. The charger was charging at 13.5 and the V reading at the batt was 13.65. I switched the setting to AGM. Charging rate went down to 13 and after the dust settled the batt V reading is 13.15 which looks to be right in the sweet spot.
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Old 12-06-2021, 04:37 PM   #9
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... This charger will raise the voltage every month for a few minutes to help boil off any sulfation which tries to grow. ...
This effect produced by some battery chargers is sometimes useful for flooded cell batteries. The "boiling" is actually production of hydrogen produced by forcing current through a lead acid battery that the battery cannot absorb. "Boiling" consumes water.

The "boiling" stirs the electrolyte which tends to stratify under certain conditions or when pure water is added to the top of dense sulfuric acid.

This process is often detrimental to AGM batteries. AGM batteries do not have a reservoir of sulfuric acid that needs to be stirred. The acid is held in a fiber pad between the plates. Stratification does not occur and you cannot add water to an AGM battery.

It is detrimental to AGM batteries when the volume of hydrogen gas exceeds the battery chemistry's ability to recombine the hydrogen with oxygen to make water. The excessive hydrogen is vented and is permanently lost. Some AGM's are capable of recombining higher volumes of gas than others.

Sulfation is a different issue. Lead acid battery chemistry dissolves lead from one set of plates, combines it with a sulfur ion from the sulfuric acid electrolyte and deposits the sulfate on the other set of plates. Electrons flow from one set of plates though external circuits to the other plate.

The deeper a lead acid battery is discharged, the thicker the sulfate coating becomes on the one set of plates. Recharging reverses the process depositing lead back onto the original set of plates.

Lead sulfate slowly forms crystals. The thicker the layer, the larger the crystals. The longer the sulfate sits, the bigger the crystals get.

Lead sulfate crystals are slower to redissolve during recharging. Large crystals tend to be left behind as the single molecules redissolve faster. Sometimes the crystals fall off the plates and accumulate in the bottom of the battery.

Heavy layers of large crystals may resist being redissolved at all. This of course leads to totally dead batteries.

Applying high voltage to sulfated batteries can under the right conditions redissolve some of the crystals that are still attached to plates. On the other hand applying high voltage to already fully charged well maintained batteries cannot dissolve crystals because there aren't any crystals.

This process only works if the batteries have been left in a discharged state for a while before recharging.

There may be other effects of forcing current through lead acid batteries that I do not know about. I know the Lifeline AGM battery manufacture recommend a "conditioning" charge for brief periods. I do not know why.
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Old 12-06-2021, 05:14 PM   #10
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I believe you did good. Occasionally cycling the batteries to 80% state of charge and then charging back to 100% is better than remaining on float for months with no activity.
Do any battery manufactures support that statement ?
I dont recall ever reading that.
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Old 12-06-2021, 06:13 PM   #11
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Do any battery manufactures support that statement ?
I dont recall ever reading that.


I have read it in many places over the years. Here are just a couple of references I found quickly. I’m sure better and more references can be found with additional searches.

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Old 12-07-2021, 06:43 AM   #12
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This has been a fruitful learning experience for me. Thanks to those who replied to my original question. The info learned here will help my new batteries live a long and happy life.
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Old 12-07-2021, 07:54 AM   #13
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I have read it in many places over the years. Here are just a couple of references I found quickly. I’m sure better and more references can be found with additional searches.

Attachment 350824
Attachment 350825
Attachment 350826
I searched 3 battery manufactures, Lifeline, Full River and Trojan. Didn't you?

None of them mention what you suggest. Full River says you can float charge a battery indefinitely .

Your articles are opinion pieces and probable all copied from one source.
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Old 12-07-2021, 08:01 AM   #14
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I searched 3 battery manufactures, Lifeline, Full River and Trojan. Didn't you?

None of them mention what you suggest. Full River says you can float charge a battery indefinitely .

Your articles are opinion pieces and probable all copied from one source.


Even my Magnum charger does this…. Shuts off when full charge and then lets the batteries discharge a bit before resuming the charge.

UPS systems for computers, etc, do this monthly to test the batteries. Granted, it also helps to verify the state of the batteries.
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