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Old 12-05-2019, 11:07 PM   #1
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Bad battery? or bad converter?

I've got a used 2017 Airstream Sport 16 that we bought used. The battery has never really worked, I assumed this was because it was left unmaintained for a while as it was being sold by the dealer we bought it from.

However, this past week I decided to finally get the battery replaced. It had an Interstate SRM-24 and I replaced it with an SRM-31 to try and get a little extra battery life out of it.

After getting it installed we drove straight to the camground we were staying (Friday night) and hooked everything up until Sunday morning when we left. This is when I noticed an issue.

We moved about five minutes away from the campground to a parking lot and I noticed the battery life was sitting at 11.9V on the battery monitor. The Use/Store switch had been set the Use the entire time we were at the campground so I believe it should have been fully charged or close to fully charged. It was around 15F when I checked the battery temp and was cold most of the time we were at the RV park.

Later that day we drove home (about 5 hours) and I noticed the battery had jumped up to around 12.3V on the battery monitor when we get back. After some research I came to the conclusion that it might be a bad converter. So I got a multimeter to test this theory.

When plugged into 15A standard home power it reads 13.6V at the battery which suggests to me the converter is working fine. If I disconnect that power it dropped to 12.6V immediately, and then seemed to slowly drop to around 12.3V after an hour. It's much warmer at home around 40F at night right now.

Does this seem normal or is the battery bad? I want to make sure to return the battery if it is bad. Could there still be an issue with the converter? Was the really low battery reading just because of the temperature.

Thanks for the help.
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Old 12-06-2019, 09:13 AM   #2
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Sounds like a bad battery to me. Since you got 13.6V when plugged into shore power, the converter is working. Additional information that would be helpful to diagnose the issue would be to know what the amp draw was when the battery dropped from 12.6V to 12.3V in an hour. Was anything using battery power? Is your inverter turned off? Are all lights inside compartments turned off? Is the radio off . . .

Dropping 0.3V in an hour may not be an issue as batteries that are being charged have a surface charge that quickly dissapears. My batteries may read 12.9V after removing the charger and drop to 12.6V quickly with a small load which removes the surface charge. Also, you only have a single battery and I'm used to dealing with a pair of batteries.

So, I suspect a bad cell in the new battery, but I don't have enough information about your situation or experience with a single battery Airstream to know for sure. I'm sure uncle_bob will chime in with his thoughts too.
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Old 12-06-2019, 09:23 AM   #3
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Quote:
Originally Posted by jeffjacka View Post
[snip]...After getting it installed we drove straight to the camground we were staying (Friday night) and hooked everything up until Sunday morning when we left. This is when I noticed an issue.
Battery voltage will drop when it gets cold, that's normal.

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Originally Posted by jeffjacka View Post
We moved about five minutes away from the campground to a parking lot and I noticed the battery life was sitting at 11.9V on the battery monitor. The Use/Store switch had been set the Use the entire time we were at the campground so I believe it should have been fully charged or close to fully charged. It was around 15F when I checked the battery temp and was cold most of the time we were at the RV park.

Later that day we drove home (about 5 hours) and I noticed the battery had jumped up to around 12.3V on the battery monitor when we get back. After some research I came to the conclusion that it might be a bad converter. So I got a multimeter to test this theory.

When plugged into 15A standard home power it reads 13.6V at the battery which suggests to me the converter is working fine. If I disconnect that power it dropped to 12.6V immediately, and then seemed to slowly drop to around 12.3V after an hour. It's much warmer at home around 40F at night right now.

Does this seem normal or is the battery bad? I want to make sure to return the battery if it is bad. Could there still be an issue with the converter? Was the really low battery reading just because of the temperature.

Thanks for the help.
Your battery can be charged from your tow vehicle through the umbilical cord, many of them are set up that way. When the drain is removed from a battery it will also recover to a higher voltage. When you plugged in at home it shows the converter is charging the battery and the charge voltage is always higher than the battery's full charge. After charging is complete you should wait about an hour before checking the voltage to get an accurate reading. It should not drop after that (with no load). If it does the battery may have a bad/weak cell.

I would take the battery back and get a replacement, looks like it's weak. All batteries have a manufactured date stamped on them. Don't buy/accept a battery that is more than 3 months old. Ideally, it will be no more than 5 weeks of your purchase. You can Google the brand of battery on how to read the date code.
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Old 12-06-2019, 09:58 AM   #4
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Hi

One battery for a trailer is not a lot of amp hours. First thing to check is what sort of drains there are on the battery. This or that here or there could make a big difference.

Biggest thing to check on a used trailer is how the use/store relay is set up. If the battery goes up to 13.x with the converter on in the use position, that's fine. Next check the store position. If it also goes up to 13.x there that's ideal in my book. It sounds like you have already checked this.

Battery voltage goes *up* when it's cold out and *down* when it's hot. A battery at 30 or 40 degrees and 12.3V is dead / near dead. The stock chargers do not have temperature compensation. They struggle to charge a battery fully when it's cold.

All that said, it does sound like a bad battery.

Bob
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Old 12-06-2019, 10:09 AM   #5
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It is possible this is an instrumentation issue. Read the voltage at the battery with the multimeter and with the status panel when charging and when not. The multimeter reading and the status panel reading should be the same. Are they?

The charge voltage of most converters of 13.6 is a compromise and may never get a battery to full charge. The initial charging should be done at around 14 volts but few converters, particularly single or dual stage ones, do that.
https://www.progressivedyn.com/rv/ch...echarge-curves



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Old 12-06-2019, 12:38 PM   #6
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Originally Posted by uncle_bob View Post
Battery voltage goes *up* when it's cold out and *down* when it's hot. A battery at 30 or 40 degrees and 12.3V is dead / near dead.
Bob

Isn't that backwards? Otherwise it would be easier to start a car at -10 than it would be at +90F. The chart I attached to my previous post shows a battery at 12.2 volts at 30F is 100% charged.
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Old 12-06-2019, 03:02 PM   #7
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Originally Posted by AirMiles View Post
Sounds like a bad battery to me. Since you got 13.6V when plugged into shore power, the converter is working. Additional information that would be helpful to diagnose the issue would be to know what the amp draw was when the battery dropped from 12.6V to 12.3V in an hour. Was anything using battery power? Is your inverter turned off? Are all lights inside compartments turned off? Is the radio off . . .

So, I suspect a bad cell in the new battery, but I don't have enough information about your situation or experience with a single battery Airstream to know for sure. I'm sure uncle_bob will chime in with his thoughts too.
I'll do some additional testing ASAP and get answers for you there, I do remember I didn't have any of the lights on and I believe I turned the radio off. And I definitely unplugged the Airstream Connect we have in the trailer.

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Originally Posted by uncle_bob View Post
Hi

One battery for a trailer is not a lot of amp hours. First thing to check is what sort of drains there are on the battery. This or that here or there could make a big difference.

Biggest thing to check on a used trailer is how the use/store relay is set up. If the battery goes up to 13.x with the converter on in the use position, that's fine. Next check the store position. If it also goes up to 13.x there that's ideal in my book. It sounds like you have already checked this.

Battery voltage goes *up* when it's cold out and *down* when it's hot. A battery at 30 or 40 degrees and 12.3V is dead / near dead. The stock chargers do not have temperature compensation. They struggle to charge a battery fully when it's cold.

All that said, it does sound like a bad battery.

Bob
I don't think I did a good job of checking the different between the use/store on the battery, I'll make sure to do this. Ideally I would love to upgrade the total AH in the trailer. I came across the LifeBlue low temp batteries which I think would be ideal for me as I'm in cold temps during the winter a lot. Any experience with these? I'm fairly certain I will move to lithium eventually but didn't feel like taking that big step this time. If the built in converter doesn't work well in the cold, I'm assuming I should probably upgrade the converter now. I'm hoping to spend some in the trailer this winter where I will only be able to run a generator and charge during the day, but so I'd like to have enough power to keep the heat running throughout the night. I'm also not sure how much battery power is enough, I'm worried about adding too much tongue weight to my trailer. But it seems like with that low temp battery, I could get a metal battery box with a lock and not try to find a place to stuff a battery in an already very small trailer.

Quote:
Originally Posted by Al and Missy View Post
It is possible this is an instrumentation issue. Read the voltage at the battery with the multimeter and with the status panel when charging and when not. The multimeter reading and the status panel reading should be the same. Are they?

The charge voltage of most converters of 13.6 is a compromise and may never get a battery to full charge. The initial charging should be done at around 14 volts but few converters, particularly single or dual stage ones, do that.
https://www.progressivedyn.com/rv/ch...echarge-curves

Al
Have been looking into better converters. The boondocker series caught my eye. Ideally l'd like one that will work well with lithium when I make the switch to those.
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Old 12-06-2019, 03:50 PM   #8
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I chose the PD4655 converter over the Boondocker because the Charge Wizard Pendant allows you to force the PD4655 into 14.4V mode. This helps to quickly charge your battery bank with a generator.

I don't know how I could run my furnace from a single battery with possibly 80AH of storage. The 80AH gets cut in half as it shouldn't be discharged below 50% and then it may get cut in half again in cold weather as you describe thus leaving 20AH of usable storage. My Airstream uses 20AH per day before I turn on the furnace. I can just get by on my pair of golf cart batteries with 230AH. Golf cart batteries are designed to be drawn down to 20% state of charge providing about 180AH of usable storage. Cut that in half due to cold weather and you still get 90AH of usable storage which is just enough for me to get through the night with the furnace running.
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Old 12-06-2019, 11:53 PM   #9
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Originally Posted by AirMiles View Post
I chose the PD4655 converter over the Boondocker because the Charge Wizard Pendant allows you to force the PD4655 into 14.4V mode. This helps to quickly charge your battery bank with a generator.

I don't know how I could run my furnace from a single battery with possibly 80AH of storage. The 80AH gets cut in half as it shouldn't be discharged below 50% and then it may get cut in half again in cold weather as you describe thus leaving 20AH of usable storage. My Airstream uses 20AH per day before I turn on the furnace. I can just get by on my pair of golf cart batteries with 230AH. Golf cart batteries are designed to be drawn down to 20% state of charge providing about 180AH of usable storage. Cut that in half due to cold weather and you still get 90AH of usable storage which is just enough for me to get through the night with the furnace running.

Wow that's even worse than I would've guessed. Guess I should really look into the lithium batteries soon rather than later.
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Old 12-07-2019, 08:02 AM   #10
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Isn't that backwards? Otherwise it would be easier to start a car at -10 than it would be at +90F. The chart I attached to my previous post shows a battery at 12.2 volts at 30F is 100% charged.
Hi

https://batteryuniversity.com/learn/...w_temperatures

Cell voltage goes *up* as temperature goes down. Capacity goes down as temperature goes down. Capacity and voltage are not the same thing.

Bob
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Old 12-07-2019, 09:45 AM   #11
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Hi

https://batteryuniversity.com/learn/...w_temperatures

Cell voltage goes *up* as temperature goes down. Capacity goes down as temperature goes down. Capacity and voltage are not the same thing.

Bob
I read that article and another one at the same site. They are talking about charging rates and gassing threshold limits for different types of batteries. As it gets colder, the charging voltage per cell increases. I couldn't find anything that specifically said voltage goes up when temps go down.

I searched for 'state of charge by temperature' and found charts that, to me, contradict one another. One shows 100% charged voltage goes up as temps go down and the other chart shows charged voltage goes down as temps go down.

In any event, I think we have moved away from the OP's original question. I don't want to be guilty of thread hijacking. Should we start a new thread???
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Old 12-07-2019, 10:37 AM   #12
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I read that article and another one at the same site. They are talking about charging rates and gassing threshold limits for different types of batteries. As it gets colder, the charging voltage per cell increases. I couldn't find anything that specifically said voltage goes up when temps go down.

I searched for 'state of charge by temperature' and found charts that, to me, contradict one another. One shows 100% charged voltage goes up as temps go down and the other chart shows charged voltage goes down as temps go down.

In any event, I think we have moved away from the OP's original question. I don't want to be guilty of thread hijacking. Should we start a new thread???
Since you have not started a new thread yet, I will jump in. I don't see UB's responses because I have him on ignore. But in Chemistry we learn about something called the Nernst equation, which is a way to calculate cell voltage for the simple electrochemical reaction that makes a lead acid battery. If you are only changing temp, as you increase temp, the cell voltage goes UP. Now that says nothing about how much voltage it takes to fully charge a cell, a different issue altogether. I really do not know why it matters, in practice. If you have temperature compensation on your charger, it does what the manufacturer built it to do. If you don't have temp compensation, just ignore it and use 80F parameters.
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Old 12-07-2019, 06:51 PM   #13
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I chose the PD4655 converter over the Boondocker because the Charge Wizard Pendant allows you to force the PD4655 into 14.4V mode. This helps to quickly charge your battery bank with a generator.

I don't know how I could run my furnace from a single battery with possibly 80AH of storage. The 80AH gets cut in half as it shouldn't be discharged below 50% and then it may get cut in half again in cold weather as you describe thus leaving 20AH of usable storage. My Airstream uses 20AH per day before I turn on the furnace. I can just get by on my pair of golf cart batteries with 230AH. Golf cart batteries are designed to be drawn down to 20% state of charge providing about 180AH of usable storage. Cut that in half due to cold weather and you still get 90AH of usable storage which is just enough for me to get through the night with the furnace running.
Is this the one you were talking about? Looks like I have the WFCO-8955PEC right now.
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Old 12-07-2019, 07:07 PM   #14
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Is this the one you were talking about? Looks like I have the WFCO-8955PEC right now.
http://www.bestconverter.com/PD4655M...ote_p_616.html
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Old 12-07-2019, 08:32 PM   #15
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Ah yeah, totally forgot to include the link in that last one...
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Old 12-07-2019, 10:39 PM   #16
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If you are only changing temp, as you increase temp, the cell voltage goes UP. Now that says nothing about how much voltage it takes to fully charge a cell
Larry
That's my understanding. Temperature increases cause cell voltage to go up, temperature decreases cause cell voltage to go down. According to the chart I referenced, a 100% charged battery at 80 F will be 12.7v. Take the temperature down to 30F and the voltage will be 12.2v but will still be 100% charged.

I upgraded my OEM converter to a Progressive PD4655.
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Old 12-08-2019, 07:11 AM   #17
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After rereading the original post, if the temperature really was 15F as stated then 11.9 Volts is about right. Resting voltage does drop as temperature drops as the posted chart indicates. It does so as a physical property of the chemical reaction taking place and the kinetics involved. That the resting voltage rose as you went home I presume is due to slightly warmer internal battery temperature of about 35F. As described the converter seems to be working fine also at 13.6 V it senses the battery is nearly fully charged. As far as I can see everything looks fine.
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Old 12-08-2019, 08:30 AM   #18
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Hi

A few more references:

http://all-about-lead-acid-batteries...re-correction/

(yes their English is a bit fractured, look at the numbers in the chart they show)

One from a battery spec sheet:

http://www.trojanbattery.com/pdf/dat...ata_Sheets.pdf

A nice easy to read chart:

https://www.solar-electric.com/media...ge-voltage.gif

If you want it from Canada:

https://www.mta.ca/uploadedFiles/Com...mpensation.pdf

If you want it in the form of a video:



Since the Nernst equation has come up, here it is:

Ecell = Eocell – (RT/zF) ln(Qr)

The key feature is the *minus sign* in front of the portion with temperature in it.... Ecell is the "what you get" Eocell is the cell under standard conditions. Voltage *does* go down with temperature.

Bob
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Old 12-09-2019, 11:33 AM   #19
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After rereading the original post, if the temperature really was 15F as stated then 11.9 Volts is about right. Resting voltage does drop as temperature drops as the posted chart indicates. It does so as a physical property of the chemical reaction taking place and the kinetics involved. That the resting voltage rose as you went home I presume is due to slightly warmer internal battery temperature of about 35F. As described the converter seems to be working fine also at 13.6 V it senses the battery is nearly fully charged. As far as I can see everything looks fine.
That was a conservative guess, it was probably a bit colder... so yeah this seems to explain the issue. Thanks for the help everyone!
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