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Old 06-08-2021, 02:44 PM   #1
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Batteries only charge to 12.9 volts

Hi, I'm wondering if I've damaged my batteries ... when hooked up to shore power (at my house, prior to going camping) my batteries seem to top out at 12.9 volts ... thus, based on my understanding with 13v being 'full' or '100%' I'm never able to get a 'full' charge ...

Should I replace my batteries or is the normal?

Thank you!
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Old 06-08-2021, 04:17 PM   #2
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Hi

What sort of batteries do you have? If they are flooded cells, first thing to do is to check the fluid levels. If they are AGM's, there is no way to do that.

How long have you let things run? It will take *hours* for the batteries to go from empty to full. A 24 hour charge is a good idea at the start of the season.

How are you checking the voltage? The stock voltmeters *do* go nutty. Best to check at the battery terminals with a multimeter. If you don't have one yet, head over and spend $30 on one. ( Yes, you can spend more and get better versions, a $30 meter will do just fine in this case).

What happens if you disconnect one battery? What happens if you disconnect the other? ( assuming you have two ). If the voltage pops up when you disconnect one ... yup... that's a battery problem.

If you still are wondering, pull the batteries and take them over to get tested. This could easily be a blown converter / charger ....

If you do replace the batteries ( .... if you have two ...), you should replace both of them at the same time.

Lots of twists and turns ... sorry about that !!

Bob
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Old 06-08-2021, 06:47 PM   #3
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You did not mention what type of batteries you have. Assuming your camper is plugged in, and you unplug it and then immediately read that you are at 12.9 v, you are reading your batteries with a draw on them that drops the voltage (all the background stuff such as refrigerator, propane detector, etc.).

I have AGMs and at 100% charge, they will read 12.9 volts when I disconnect.

To get an accurate fully charged voltage, you would pretty much have to disconnect the batteries and then take a voltage reading to see an accurate charge state based on volts.
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Old 06-08-2021, 08:10 PM   #4
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12.8-12.9v is a very good thing for lead acid batteries. Technically 12.6v at rest with no loads is "full" for most brands.
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Old 06-08-2021, 08:32 PM   #5
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I've got 2 new Interstate flooded batteries. I know that once they come off the charger and sit for a bit they settle down to 12.9 volts.

Jack
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Old 06-09-2021, 07:40 AM   #6
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Quote:
Originally Posted by uncle_bob View Post
Hi

What sort of batteries do you have? If they are flooded cells, first thing to do is to check the fluid levels. If they are AGM's, there is no way to do that.

How long have you let things run? It will take *hours* for the batteries to go from empty to full. A 24 hour charge is a good idea at the start of the season.

How are you checking the voltage? The stock voltmeters *do* go nutty. Best to check at the battery terminals with a multimeter. If you don't have one yet, head over and spend $30 on one. ( Yes, you can spend more and get better versions, a $30 meter will do just fine in this case).

What happens if you disconnect one battery? What happens if you disconnect the other? ( assuming you have two ). If the voltage pops up when you disconnect one ... yup... that's a battery problem.

If you still are wondering, pull the batteries and take them over to get tested. This could easily be a blown converter / charger ....

If you do replace the batteries ( .... if you have two ...), you should replace both of them at the same time.

Lots of twists and turns ... sorry about that !!

Bob
Hi, Yes, I have two AGM Group 24 12v batteries in parallel. This morning I disconnected the shore power, turned off the battery usage switch (located in my trailer) and then used a multi-meter to check voltage. I get 13.06 on one battery and .. 13.1 on the other ... which is super cool (I suppose!) as this must mean my batteries are 'ok'.

Now however, the 'battery level' check in the trailer (when pressed) reads 12.6 (this with everything turned off and no shore power connected).

Why would by SeeLevel display not know the correct voltage on my batteries?
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Old 06-09-2021, 07:50 AM   #7
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Quote:
Originally Posted by El Juncal View Post
Hi, Yes, I have two AGM Group 24 12v batteries in parallel. This morning I disconnected the shore power, turned off the battery usage switch (located in my trailer) and then used a multi-meter to check voltage. I get 13.06 on one battery and .. 13.1 on the other ... which is super cool (I suppose!) as this must mean my batteries are 'ok'.

Now however, the 'battery level' check in the trailer (when pressed) reads 12.6 (this with everything turned off and no shore power connected).

Why would by SeeLevel display not know the correct voltage on my batteries?
Once the batteries are fully charged and disconnected from everything you need to let them rest an hour or more for an accurate un-loaded reading. They are probably not over 13 volts but 12.6-12.9 as mentioned which is right where they should be. The See Level device puts a load on the batteries as well as the battery switch being on can allow for other loads to be present. Also the See Level battery monitor is not the greatest and will be affected by loads, a true shunted battery monitor is best if you want to know exactly where you are at.
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Old 06-09-2021, 07:55 AM   #8
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As mentioned above, I think your batteries are fine. My AGMs tend to show 13.6V when connected to shore power, but after I disconnect and they settle down, they show 12.9V.
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Old 06-09-2021, 11:51 AM   #9
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My fairly new flooded lead acid top out at about 12.7 after relaxing from a full charge. I’d say 12.9 is unusual unless you just shut off charging.
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Old 06-09-2021, 02:10 PM   #10
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Originally Posted by El Juncal View Post
Hi, Yes, I have two AGM Group 24 12v batteries in parallel. This morning I disconnected the shore power, turned off the battery usage switch (located in my trailer) and then used a multi-meter to check voltage. I get 13.06 on one battery and .. 13.1 on the other ... which is super cool (I suppose!) as this must mean my batteries are 'ok'.

Now however, the 'battery level' check in the trailer (when pressed) reads 12.6 (this with everything turned off and no shore power connected).

Why would by SeeLevel display not know the correct voltage on my batteries?
Hi

The SeeLevel stuff can be wrong for a variety of reasons. The simplest one is that they do break ....Being off by 0.2V in either direction is not that unusual.

Bob
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Old 06-09-2021, 02:55 PM   #11
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Originally Posted by El Juncal View Post
Hi, Yes, I have two AGM Group 24 12v batteries in parallel. This morning I disconnected the shore power, turned off the battery usage switch (located in my trailer) and then used a multi-meter to check voltage. I get 13.06 on one battery and .. 13.1 on the other ... which is super cool (I suppose!) as this must mean my batteries are 'ok'.

Now however, the 'battery level' check in the trailer (when pressed) reads 12.6 (this with everything turned off and no shore power connected).

Why would by SeeLevel display not know the correct voltage on my batteries?
There are a variety of reasons. The long run, from the batteries to the wall location offers resistance. Each connection in that run offers more resistance. The circuit to the SeeLevel (in my unit) runs from the battery, through a breaker to the positive buss bar, to distribution panel then out on a non-dedicated circuit....some 24 feet or so to the rear of the SeeLevel. All of that creates a voltage drop, due to resistance.
All that said, mine only shows a 0.1V drop when compared to my Victron and Tri-Metric readings.
My anal retentive nature would make me hunt for the cause of your difference.
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Old 06-09-2021, 03:08 PM   #12
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As mentioned above, I think your batteries are fine. My AGMs tend to show 13.6V when connected to shore power, but after I disconnect and they settle down, they show 12.9V.
If you are using the See Level or similar device, or a multimeter, you are seeing the charging voltage, not the actual battery voltage.
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Old 06-09-2021, 03:23 PM   #13
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12.8-12.9v is a very good thing for lead acid batteries. Technically 12.6v at rest with no loads is "full" for most brands.
I would agree ....on my sea level I get up around 13.6 while charging and around 12.6-12.7 at rest after a charge.
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Old 06-10-2021, 06:20 AM   #14
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Even with your switch in the store position, your propane detector stays on, potentially other draws, which means you are not getting a true "at rest" reading like you did when you disconnected the batteries.

I have a Merlin Smartgauge with dedicated cables to the battery terminals, and it always gives me a higher voltage reading than the Airstreams built in voltage gauge...I suspect for the reason others have said, length of run, resistance in connections etc.
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Old 06-10-2021, 06:24 AM   #15
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If you are using the See Level or similar device, or a multimeter, you are seeing the charging voltage, not the actual battery voltage.
Iím not. Iím using a Zamp charge controller that shows battery state of charge.
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Old 06-13-2021, 09:11 AM   #16
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If not mistaken, When connected to shore power, the battery charge rating your seeing is being controlled by your inverter/charger.
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Old 06-13-2021, 09:50 AM   #17
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Using voltage alone to determine state of charge is flawed unless you allow the batteries to rest, not charging or discharging, for several hours. A shunt is a much better tool to monitor batteries so you can see amp hrs in and out.
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Old 06-13-2021, 12:04 PM   #18
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Depends on the battery, how it's connected, how you measure, and the charger. I have found most chargers will not charge a deep cycle battery beyond 12.9 volts. The same chargers will charge a good automotive battery to between 13.1 and 13.7 volts
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