what is the accurate way to test house batteries?

[Sir Traveller]

Hello Everyone…

I have a 2003 Ford F-53 RV

What’s the most accurate way to test house batteries using multimeter and hydrometer? Disconnect from shore power then keep few lights on inside the RV to give a bit of load? Do I have to disconnect the 2 batteries from each other and test each one separately? or no need to disconnect anything ?
I appreciate any suggestions…

[boondocking]

If testing for percentage of charge use a hygrometer. If testing for load, need to have them load tested. Putting a load on them and using a multimeter won't be accurate.

[NJKris]

and at least a half hour after charging for surface charge to dissipate. If it's longer than that, I'm sure somebody will correct me.

[TitanMike]

Originally Posted by NJKris

and at least a half hour after charging for surface charge to dissipate. If it's longer than that, I'm sure somebody will correct me.

Letting the battery sit as you said is one way.

If in a hurry just turn a bunch of 12v appliances for 10 minutes or so and the surface charge will dissipate quickly. Then read voltage and consult a chart for %SOC.

Old school load testers had instructions to just push load button and watch voltage. It would drop fairly steady at first then stay steady. As soon as it stopped dropping you released the load button, waited until voltage rose and again stabilized. THEN you looked at the SOC on the meter which was usually just segments in green, yellow, and red.

[Trawlerphil]

Harbor Freight makes an inexpensive "load tester".
https://www.harborfreight.com/500-am...ter-91129.html

[AudiDudi]

I use my refractometer to tell what the status of the batteries are. Also a digital volt meter for a voltage reading. It doesn't cost much more than a good hydrometer and tests other things also. For a tad over $20, it is a very handy tool.

https://www.amazon.com/Antifreeze-Co...s%2C305&sr=8-3

[camaraderie]

Originally Posted by NJKris

and at least a half hour after charging for surface charge to dissipate. If it's longer than that, I'm sure somebody will correct me.

The standard for testing a static charge is 24 hours after removing from all charging and loads.
The quickest way to take a reading is to get a $20 dummy load tester from harbor freight. No waiting.

[awellis3]

Originally Posted by Sir Traveller

What’s the most accurate way to test house batteries using multimeter and hydrometer?

Put the multimeter back in the toolbox and use a temperature-adjusted hydrometer.

[Harkerr]

Auto stores or Wal Mart have digital load testers.

[TitanMike]

Originally Posted by awellis3

Put the multimeter back in the toolbox and use a temperature-adjusted hydrometer.

Good advice --------unless your batteries are AGM

[Sir Traveller]

So I disconnected the shore power and turned off the house battery switch, I tested the batteries, and the measurements were as follows: the voltage ( using a millimeter was 12.83 , and when I used the hydrometer, the first battery tested 1.3 and the second battery 12.65 , are these too high? Is it possible to be because of overcharging?

[camaraderie]

Originally Posted by Sir Traveller

So I disconnected the shore power and turned off the house battery switch, I tested the batteries, and the measurements were as follows: the voltage ( using a millimeter was 12.83 , and when I used the hydrometer, the first battery tested 1.3 and the second battery 12.65 , are these too high? Is it possible to be because of overcharging?

Well you did not disconnect your battery negative wire...thowing the house battery switch is not the same...and you did not mention waiting 24 hours with it disconnected so you electrical measurements are worthless.

As to your Hydrometer readings.
1. There should be 12 not 2 readings
2. They need to be temperature adjusted.[ Add or subtract four points (.004) to your reading for every 10 F (6 C) registered above or below 80 F]
3. They appear to have been taken immediately after charging with
no time for surface charge to dissipate. Needs at least a couple of hours.
4. Assuming you added distilled water...you need to charge & discharge to 50% and charge again to get proper mixing for a reading. If you didn't add water and just charged fully...then once you WAIT long enough EACH cell in a battery should read 1.265 and if not...then ALL CELLS must be within 25 points of one another.
i.e. if one is at 1.265...then no cell should be below 1.240


As it stands...nothing accurate can be said about your battery but since it seems to have been fully charged....a simple thing to do would be to remove the negative wire from them for 24 hours and test voltage with your meter. It it remains at 12.6-12.7 then it has taken a full charge.
You should be good. Anything less = loss of capacity or battery damage.

[Bogieboy]

get one of these, or similar and be done with guessing... https://www.amazon.com/KONNWEI-100-2.../dp/B08MPXGSGN

[camaraderie]

Originally Posted by Bogieboy

get one of these, or similar and be done with guessing... https://www.amazon.com/KONNWEI-100-2.../dp/B08MPXGSGN

Neat device and nicely priced! I do note that you MUST know the CCA rating of your batteries and input it for it to work right.
This is often an unknown number on deep cycle batts so if you plan to order one...make sure you can get the number!

[Bogieboy]

Originally Posted by camaraderie

Neat device and nicely priced! I do note that you MUST know the CCA rating of your batteries and input it for it to work right.
This is often an unknown number on deep cycle batts so if you plan to order one...make sure you can get the number!

most all of the deep cycles batteries i have had show a "marine" cranking amps, which is equivalent to a CA test, instead of the cca test, difference simply being the rating at 32F or above(CA) or at 0 degrees Fahrenheit (CCA).

[Bogieboy]

also, here is a quick and easy formula from Interstate, "To calculate the MCA rating of a battery compared to its CCA rating, multiply by 1.25."

so, to go the other way, just divide the MCA, marine cranking amps, by 1.25 to find your CCA, if the battery does not display it, or your tester does not read MCA.

[Sir Traveller]

many thanks to all who participated, I appreciate all your ideas and suggestions