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Old 10-13-2017, 05:08 PM   #21
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2002 30' Classic S/O
Fleming Island , Florida
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Batteries, particularly old batteries, batteries subjected to misuse or shock, develop internal leakage. Those currents obviously do not go through the shunt. Sulfated batteries lose capacity. Charge the batteries with shore power for several days, measure the voltage and then disconnect them. Under charge a fully charged battery should read over 13 volts. Measure the specific gravity with a hydrometer. A fully charged battery should read around 1.250. All cells should be within .050 of each other. Let them sit for a couple of days and check voltage and specific gravity again. A severely declined cell could indicate internal leakage and the battery should be replaced. If the battery reads good, somehow you have a phantom load.

In my experience a parts house load test only proves starting capacity and is not indicative of the batteries ability to hold a charge.

Al
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Old 10-13-2017, 06:26 PM   #22
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2017 30' Classic
2022 Interstate 24X
Carlisle , Pennsylvania
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Hi

We now seem to have more than one set of batteries involved.....

So, if you want a definitive test, here's how to do it:

Pull the batteries from the trailer. Put them on a proper charger and monitor what's going on. Most good shops should have a charger that will give you a readout of the whole charge process. Let it run for at least 24 hours on each battery. Make sure that the charge terminates below 1A after the first 16 hours and does not "surge" after that unless the charger is in equalization mode. You do want to do this with a shop charger and not the converter on the trailer. Snap-on makes a pretty good one ....

Let the batteries sit for 24 to 48 hours and check their voltage with a good multimeter. They should be in the vicinity of 12.7V. If they are below 12.5V and it's roughly 70F, they are trash, replace them.

Now grab a handy 6A load. A two ohm resistor will do fine. You will need to dump 72W into it so it will need to be rated for > 150W. Alternatives are a proper solid state constant current load or a big chunk of copper wire in a bathtub full of oil. Strap the load on and check the voltage on the battery.

Come back every hour and log the voltage. If you need to stop overnight, that's fine. Disconnect the load and start again the next day. Keep logging voltages until you are below 12.0V.

At this point hours x 6A will give you amp hours. Twelve hours is pretty good for a group 24 at this current. You would expect a few more hours on a group 27. If you have a solid state constant current load, the numbers are easy. If you use a resistor, go through the ohm's law stuff to get the proper current for each hour. If you use a big chunk of coper wire in a bathtub full of oil, put a current meter on it ....

Once the first battery is done, hook up the second one and start testing it.

Once you are done with both, they should be within about 10% of each other. If they are significantly different, that's not good. One of them will eventually "kill" the other one.

So you now *know* what the capacity of each of your batteries actually is. Add the two of them together and program that into the monitor.

Next, charge the batteries up again.

This time set them away someplace quiet for a month. Now run the same discharge process on them. Do not recharge them first, just run the discharge the same way you did before. Note the results. If you do not have at least 90% of the capacity you did on the first test, the battery should be replaced.

So by now you do have good data on your batteries. You know the capacity. You know how much they loose in a month. You know they are matched and working well together. Time to put them back in the trailer.

Is there a shortcut that gives full data? Nope.

Bob
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Old 10-13-2017, 07:23 PM   #23
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Uncle bob:
Nice!

Al
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Old 03-08-2021, 08:32 PM   #24
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2018 30' International
Brownwood , Texas
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Quote:
Originally Posted by cazual6 View Post
I concur.
My trailer is hooked up to power circuit and I check the battery monitor and it says 15 per cent. I thought when you had outside power hooked up the batteries we’re charging?
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Old 03-09-2021, 06:01 AM   #25
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2003 25' Classic
Houstatlantavegas , Malebolgia
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Quote:
Originally Posted by GMFL View Post
Factory Battery amp hr rating is nothing more then a close estimate as to what the battery is going to have. Batteries lose storage capacity as they are used, and harsh use i.e. running dead or extremely low causes this faster. 12volt interstate grip 24 batteries are not true deep cycle battery. They are rated CCA (cold cranking amps). They are designed for faster release of their stored power.

Check the water level in the batteries and make sure that is good.

What kind of charger are you using?

Is ALL the Power being used going through the shunt?

Is the Victron set up with the correct amp hours available base on the batteries you have and not just what Interstates inflated numbers?

Simple answer is the batteries are not performing as you desire or meeting your needs so gotta change something. My bet is the batteries.

^
X2

No way do you have 10 daze left with 12.2v.

POI it took several test sessions of setting parameters to get the SOC to get a reasonable estimate of the time remaining on the Victron.
We always used 12.2 as the discharge limit with our AGM Lifelines.

Bob
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My trailer is hooked up to power circuit and I check the battery monitor and it says 15 per cent. I thought when you had outside power hooked up the batteries we’re charging?

What does it show for charge current?
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