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Old 09-28-2021, 05:13 PM   #1
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I hope this dummy (That woud be ME) didn't ruin my batteries...

I haven't checked my batteries in way too long, completely my fault. My 12v chassis batteries are AGM, they're fine. I have four 6v wet cell house batteries that are about 18 months old. They stay plugged into 110v 20a when parked to keep them charged up. When I took the coach out of storage to get it ready to go the next day, the batteries were at 13.5v (+/-) as usual. I put the coach in front of the house, and turned off the main disconnect switch so there was no draw at all on the batteries as the coach sat overnight. Next moring I turned everything back on and the batteries had dropped down to 12v just sitting there without the charger.

We just got to the RV park, and after parking I checked the water level. Thankfull no cells were uncovered but they were VERY low. Each cell took about 16 oz of distilled water. It's plugged into 50a now so they're getting a good charge, my worry is that I might have done damage letting them get that low.



Anyone have thoughts and/or experience with this?
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Old 09-28-2021, 05:31 PM   #2
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If the top of the plates were covered , the cells were not dangerously low .

How old are the batteries ?
Your 13.5 v reading was a surface charge , that was going to dissipate quickly.
12.6 . to 12.8 is a good voltage for batteries in the best of condition ; at rest ( cooled down after charging ).

Time to have the batteries load tested , even one bad cell in the battery bank can draw the whole set down overnight .
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Old 09-28-2021, 06:12 PM   #3
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No damage occurs until the voltage gets below 10.6 volts.

You only cycled then to about 40% discharge, we above the danger zone.
Check any Depth of Discharge chart.

You may have some things on that the disconnect does not shut off.

Your batteries will be fine and live a happy life. No need to test them.
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Old 09-28-2021, 06:21 PM   #4
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12.7 volts “open circuit” (disconnected) is a fully charged battery after the battery has rested for a period of time to remove the surface charge. Once the battery is connected to the RV the voltage will be lower do to loads and there is not an accurate way to measure it because of the loads.

Also the battery disconnect (salesman) may not disconnect all the loads, sometimes the alarms (LP & CO2) are connected directly to the battery for safety. The only way to be sure the battery is disconnected is by removing one of the battery leads. Typically the negative lead is disconnected for safety

If you are concern I would charge the batteries until they are in a "Float" voltage, then disconnect them for 12 to 24 hours and measure the voltage. The following is “open circuit” voltages for state of charge:

100% 12.73 Vdc
90% 12.62 Vdc
80% 12.50 Vdc
70% 12.37 Vdc
60% 12.24 Vdc
50% 12.10 Vdc
40% 11.96 Vdc
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Old 09-28-2021, 08:13 PM   #5
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Brought home 1st RV yesterday which has a pair of 6V house batteries, non-maintenance free. Opened them up to see water below top of electrodes. Battery tester indicated top of weak range weak. Filled them up (took almost 3 litres of distilled water) and charging.
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Old 09-28-2021, 08:44 PM   #6
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I would consider doing an equalization charge or two. Batteries benefit from a series of FULL cycles: fully charge (with equalize), then slow discharge to 12 volts or so, then fully charge again, and repeat. Basically by doing this you are breaking up crystallized structures on the electrodes, allowing for more efficient contact between the electrolyte and the electrode.
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Old 09-28-2021, 11:05 PM   #7
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Thanks guys - sounds like I should be ok. Glad I hopefully dodged a bullet.
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Old 10-04-2021, 08:14 PM   #8
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I just replace my pair of Interstate GC2s. I performed a load test using 7a and could only get 50ah out of the 115ah I should have. The 6v batteries were 230ah, so 50% should have given me 115.

I disconnected the batteries from series and found one of the batteries was .3 volts lower than the other… so it was drawing the set down. Time for a replacement so I went cheap and put in 2 Costco Interstate GC2 6v 210ah batteries. So far they are working great.

I figure in another year the lithium’s will be cheap enough to justify all the changes needed to convert. My Magnum MM1212 inverter/charger does not support lithium so conversion will cause replacement of that along with other components. In the short term I will add solar to keep the FLAs up.
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Old 10-04-2021, 08:25 PM   #9
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Quote:
Originally Posted by SavnTheWales View Post
I just replace my pair of Interstate GC2s. I performed a load test using 7a and could only get 50ah out of the 115ah I should have. The 6v batteries were 230ah, so 50% should have given me 115.



I disconnected the batteries from series and found one of the batteries was .3 volts lower than the other… so it was drawing the set down. Time for a replacement so I went cheap and put in 2 Costco Interstate GC2 6v 210ah batteries. So far they are working great.



I figure in another year the lithium’s will be cheap enough to justify all the changes needed to convert. My Magnum MM1212 inverter/charger does not support lithium so conversion will cause replacement of that along with other components. In the short term I will add solar to keep the FLAs up.
The batteries, if good, should have given you 230 AH down to 10.6 volts.

The load should have been about 12 amps and lasted 20 hours. 225 AH ÷ 20 Hours.

The rating is 225 AH at the 20 hour rating.

Not sure what test you did but it doesn't sound accurate, although your batteries looked bad.
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Old 10-05-2021, 06:25 AM   #10
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While on the topic of battery care

Does anyone on here have firsthand experience with a "BatteryMinder" desulfator/float charger? The dealership installed 6, Interstate AGM's for the coach when we bought it. I'd like to keep them in tip-top shape as long as possible. I've got a desulfator/charger for the 2 chassis batteries.

https://www.amazon.com/dp/B005EKY20K...v_ov_lig_dp_it
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Old 10-05-2021, 06:36 AM   #11
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Quote:
Originally Posted by MN_Traveler View Post
I would consider doing an equalization charge or two. Batteries benefit from a series of FULL cycles: fully charge (with equalize), then slow discharge to 12 volts or so, then fully charge again, and repeat. Basically by doing this you are breaking up crystallized structures on the electrodes, allowing for more efficient contact between the electrolyte and the electrode.
Is this procedure recommended periodically even if everything is in good working order?
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Old 10-05-2021, 07:24 AM   #12
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Is this procedure recommended periodically even if everything is in good working order?


Yes. Depending on how you treat your batteries ... if you are able to consistently and repeatedly bring them to Float charge condition every single time you discharge them ... then i would do the equalization say every other month or so during use, and the again after any longer storage (during which they will self discharge). If you are unable to bring them completely to float, then perhaps do it every month?

NOTE: non-sealed lead acid batteries (the ones with the caps where you add water) can be equalized. Sealed lead acid batteries can NOT be equalized (equalization gives off hydrogen gas and depletes the water level). MOST AGM batteries can NOT be equalized (they are sealed). The exception to this is Lifeline batteries ... the manufacturer of which *explicitly* recommends doing equalization charges after prolonged storage and once a month during usage (lifelines are more expensive though)
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