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Old 05-27-2018, 02:46 PM   #1
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Batteries with low voltage after 6 hours

We were boondocking this week and the first night out car batteries went to low voltage and set off the alarm within 6 hours. Everything was shut off except the controls for the propane cooled refrigerator. Any ideas on what could be draining the battery at night while everything is shut off? The batteries are almost 3 years old.

Thanks!
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Old 05-27-2018, 02:56 PM   #2
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Tough call. Chicken or egg.

First I would check the charging voltage on shore power, I e checking the inverter.

Also search for lights in compartments.

Then the fun begins.
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Old 05-27-2018, 03:35 PM   #3
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What kind of Converter/Charger do you have?

If a standard 3 stage WFCO or similar you may just have "Old Batteries" that have lost capacity due to sulfation. Converters like the Progressive Dynamic units with "Charge Wizard" add a 4th stage that forces a higher voltage into the batteries if there has been no charging activity for 30 hours. This 15 minute long de-sulfation/equalization session keeps the electrolyte from stratifying in the batteries and also prevents the sulfation "crystals" from forming hard sulfate on the lead plates which can't be converted to useful elements by charging.

Chargers that use this feature are supposed to make batteries last a couple years longer than the average (5-6 years versus 3-4 years).

Buy a battery hydrometer, fully charge your batteries, and then check and record the specific gravity reading for each cell. Your answer on the battery condition will show itself there.

Here's a chart showing state of charge, Specific Gravity, and open circuit voltages for regular lead acid battery.

Approximate
state-of-charge Average
specific gravity Open circuit voltage
2V 6V 8V 12V
100% 1.265 2.10 6.32 8.43 12.65
75% 1.225 2.08 6.22 8.30 12.45
50% 1.190 2.04 6.12 8.16 12.24
25% 1.155 2.01 6.03 8.04 12.06
0% 1.120 1.98 5.95 7.72 11.89

The 2 V information is useful if the cell connectors are exposed like on Golf Cart batteries. You can measure voltage on each cell and compare against chart.
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Old 05-27-2018, 04:39 PM   #4
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Quote:
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We were boondocking this week and the first night out car batteries went to low voltage and set off the alarm within 6 hours. Everything was shut off except the controls for the propane cooled refrigerator. Any ideas on what could be draining the battery at night while everything is shut off? The batteries are almost 3 years old.

Thanks!
There are many parasitic power drains on RVs.
CO/propane detector, clock in radio, the climate control in a Dometic fridge and so on.

Are you sure the batteries were fully charged when you parked?
Don't assume they were or that your current batteries are good.
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Old 05-27-2018, 08:11 PM   #5
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Sounds like old batteries. I would have the batteries tested.
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Old 05-28-2018, 06:06 PM   #6
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X2 on tartan mikes battery checking procedure...if you have sulphation and loss off battery capacity...it will show up via "turkey baster" hydrometer after adding distilled water as needed and FULLY charging batteries for at least 10 hours. If you see significant differences between the cell readings...best to get new ones. Here's the readings you should see from each cell in the FIRST column... (the rest are readings from a multimeter taken at least 24 hours after disconnection from everything). If you see more than a .040 difference between cell readings...you have sulfation. All cells should read OVER 1.217 for the battery to be salvagable for deep cycle use and any desulphation attempts.
Note that no temperature correction is needed if you are comparing results between cells...but that the charts reflect an 80 degree temperature for absolute state of charge readings.
Subtract 0.004 for every ten degrees when the temperature is below 80
Add 0.004 for every ten degrees when the temperature is above 80
Example...at 70 degrees 1.273 is 100% charged. At 90 degrees it is 1.281

Hope this is helpful.
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Old 05-28-2018, 06:24 PM   #7
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We were boondocking this week and the first night out car batteries went to low voltage and set off the alarm within 6 hours. Everything was shut off except the controls for the propane cooled refrigerator. Any ideas on what could be draining the battery at night while everything is shut off? The batteries are almost 3 years old.

Thanks!
Terminology. Not car batteries.. either chassis batteries (start and run engine and rig) or coach batteries.

You are talking about the coach batteries, which if they are original, and 3 years old, are very likely bad, especially since their usage is unknown. Other issues may be also here like the charging system from the vehicle, etc. but if the frig was on propane, and nothing else was on ex. Parasitic loads, the batteries should have lasted at least one night.

Start there, and get a volt meter so you can at least check the battery voltages, if you don't have a readout. Battery monitor like a Victron would be nice if you are boondocking regularly.
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Old 05-28-2018, 07:53 PM   #8
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Quote:
Originally Posted by 125992 View Post
We were boondocking this week and the first night out car batteries went to low voltage and set off the alarm within 6 hours. Everything was shut off except the controls for the propane cooled refrigerator. Any ideas on what could be draining the battery at night while everything is shut off? The batteries are almost 3 years old.

Thanks!
My first battery mistake when dry camping was to think the batteries would be fully charged from the two hour drive to camp. Wrong. Next I thought dead batteries when I picked it up at storage,. No problem. Just charge them overnight. Wrong.

Batteries are an ongoing job. (Unless you have big solar like we do.).

If the the batteries haven't had perpetual and ongoing maintenance the probably bad. If you've been diligent about keeping them charged and keeping them watered then there could be system problems as everybody has been describing. If the batteries were actually good and well maintained then something is pretty a pretty big demand to take them down in 6 hours. I would look at inverter. Do you have one? If so It needs to be turned off at night as the ambient draw of a murder is fairly High even when nothing is using it would more likely than not with 6 hour battery life something has been using it like your refrigerator automatically switching over to Electric or your water heater inadvertently being left on electric.

Remember batteries that have been badly depleted do not fully charged in an hour or two hours. Unless you've built yourself an extremely heavy duty power converter charger, you probably need stock Factory charger to have current for 6 or 8 hours a day to maintain the batteries. A lot of things going through it best of luck finding them. God bless solar I haven't had to think about this stuff in several years now.
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Old 05-28-2018, 08:11 PM   #9
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A note on batteries. You need to pay attention regularly to batteries, especially deep cycle batteries you will expect to at least last overnight.

My trailer is just under a year old as are the batteries. Today was "Maintenance day" for the batteries. Checked the electrolyte level on all 12 cells (2 12V batteries in parallel) then checked specific gravity in each cell, recording the readings. All cells, with the exception of ONE, read a SG of 1.280 +/- .005. The one cell, even after several re-checks, read 1.235 or "45 points" low. The battery containing that cell is now undergoing an equalization charge. Tomorrow it will be checked again and if it doesn't correct itself a new battery will be on the menu soon.

That low cell essentially limits the battery to about 75% if it's fully charged capacity and experience has shown me that unless equalization corrects it, it will get worse in short order.


BTW, I like to be able to isolate my batteries with a battery selector switch for situations just like this. When one of the batteries needs an equalization charge, no point in over-cooking the good battery while applying the "equalization charge" to the one with the low cell.
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Old 05-29-2018, 08:40 AM   #10
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I keep testing our coach batteries,,, they test good,,,
even though I don't think that are !!!
We boondock one day a year,,, not sure I want to spend some $200 for new batteries ???
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Old 06-01-2018, 09:11 AM   #11
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Dual Use Batteries

One problem is that most RVs come with compromise batteries. If it lists CCA (Cold Cranking Amps) then it isn't a true deep cycle. if it doesn't start your vehicle, you want a true deep cycle. I've been very unimpressed with my batteries, and plan to replace them with two 6v Golf Cart Batteries from Costco ($85 each). You have to wire them in series instead of parallel, but they are true deep cycle, and at that price I don't know how you can go wrong.
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Old 06-01-2018, 12:29 PM   #12
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Originally Posted by mnoland30 View Post
One problem is that most RVs come with compromise batteries. If it lists CCA (Cold Cranking Amps) then it isn't a true deep cycle. if it doesn't start your vehicle, you want a true deep cycle. I've been very unimpressed with my batteries, and plan to replace them with two 6v Golf Cart Batteries from Costco ($85 each). You have to wire them in series instead of parallel, but they are true deep cycle, and at that price I don't know how you can go wrong.

When using dual purpose Marine batteries that don't have Amp Hours listed just use the "Reserve Capacity" number. This is determined using a 25 amp rate. To avoid damaging the battery by over discharging cut the reserve number in half for a single battery. If the reserve capacity is 210 minutes, that battery will deliver 25 amps for just under 2 hours before hitting the 50% mark.

Most travel trailers won't have a 25 amp draw continuously however. a couple amps for lights, a few more for stereo or TV, and intermittent use of water pump is more like it although running a furnace can run that up by another 5-6 amp.

Naturally, if you have two equally sized batteries the capacity doubles to maybe 4 hours of continuous draw and more if only intermittent.

On my trailer I have monitored two Interstate SRM-29's (Provided at no cost by Dealer) and in a 5 day stretch with no recharging, my max power draw was only 44 amp hours. (out of 240 amp hours total for the two batteries).

Monitoring was done with a Victron BMV 702 which has been one of the best upgrades I've added.
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