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Open Roads Forum  >  Class A Motorhomes  >  Maintenance Issues & Tips

 > best way to test house batteries ?

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Sir Traveller

La Mesa Southern California

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Posted: 02/12/21 04:26pm Link  |  Quote  |  Print  |  Notify Moderator

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…

theoldwizard1

SE MI

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Posted: 02/12/21 04:44pm Link  |  Quote  |  Print  |  Notify Moderator

For the most accurate results disconnect the batteries from EVERYTHING. If you have two 12V batteries in parallel disconnect them. Using a separate charger, charge completely. This might take 24 hours or more.

Disconnect the charger and let the batteries "rest" for about 30 minutes. Check and record the voltage of both batteries. Without connecting shore power, connect ONE battery and turn all interior lights. Better yet, buy a Harbor Freight battery load tester (LED lights can not generate enough load). Follow direction with the load tester. With lights you will have to leave them on for 15-30 minutes. Record the voltage at the battery.

After charging and resting the battery voltage should be about 13.2V.

After the load has been removed the batter voltage should be above 12V.

MountainAir05

New Mexico

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Posted: 02/12/21 04:53pm Link  |  Quote  |  Print  |  Notify Moderator

I test with them separate. Then check each with the hydrometer after they set for an hour or so. I also check each cell with the volt meter after the hydrometer test. Between the hydrometer and volt reading of each cell you will find any weak or dead cells. Your lights will not put a load on the system. Load meters are $25 or so. I only use that if I am having a issues on the weak cells.

If you battery charges up good but will not hold voltage after 4 hours then you have a weak/dead cell. Should drop close to 2+ volts for a weak cell. A weak cell battery will pull any battery that it is connected to down.

pianotuna

Regina, SK, Canada

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Posted: 02/12/21 06:09pm Link  |  Quote  |  Print  |  Notify Moderator

Charge the batteries fully. Disconnect them from the RV. Disconnect them from each other. Wait 24 hours. Check the voltage. Check with a good temperature compensated hydrometer.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, soon to have SiO2 batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

dieseltruckdriver

Black Hills of SD

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Posted: 02/12/21 06:27pm Link  |  Quote  |  Print  |  Notify Moderator

Another option is to find a shop with one of these.
Sometimes auto parts stores will have one.

I use one at work, and almost never touch a hydrometer when I need to PM batteries. A hydrometer is MUCH cheaper though.


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opnspaces

San Diego Ca

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Posted: 02/13/21 08:28am Link  |  Quote  |  Print  |  Notify Moderator

MountainAir05 wrote:

I test with them separate. Then check each with the hydrometer after they set for an hour or so. I also check each cell with the volt meter after the hydrometer test.

How do you check an individual cell with a volt meter?


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garyemunson

Reno, Nevada

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Posted: 02/13/21 08:33am Link  |  Quote  |  Print  |  Notify Moderator

https://www.harborfreight.com/100a-612v-battery-load-tester-61747.html?_br_psugg_q=battery+tester

wopachop

Who run bartertown

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Posted: 02/13/21 08:50am Link  |  Quote  |  Print  |  Notify Moderator

Sir Traveller wrote:

What’s the most accurate way to test house batteries using multimeter and hydrometer?
Depends what you are trying to test. The hydrometer works great to determine how much of a charge the batteries will accept. Which will also give a rough idea of capacity remaining for the batteries.

It wont really tell you the voltage drop under load. For that you could buy a load tester. Or you could load test at home. Put a multimeter on the batteries and then have someone flip on lights and run the water pump. Note how much voltage drop occurs. I dont want to give out voltage numbers because i dont know the correct numbers to give. But lets say you turn on the water pump and your voltage drops to 11.9V. That would indicate the batteries are getting older and sagging too much under load.

pianotuna

Regina, SK, Canada

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Posted: 02/13/21 08:53am Link  |  Quote  |  Print  |  Notify Moderator

wopachop,

If the owner has an inverter, that is an easy way to ramp up to quite a high load, especially if each battery is tested as an individual.

MountainAir05

New Mexico

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Posted: 02/13/21 09:44am Link  |  Quote  |  Print  |  Notify Moderator

opnspaces wrote:

MountainAir05 wrote:

I test with them separate. Then check each with the hydrometer after they set for an hour or so. I also check each cell with the volt meter after the hydrometer test.

How do you check an individual cell with a volt meter?


Saves writing and it has a video. Wash off the lead when you are finish.

https://www.youtube.com/watch?v=_8qgZoovWHI&ab_channel=BatteryChem%E2%84%A2LeadAcidBatteryDesulfatorandReconditioner

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