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Old 06-05-2020, 10:21 AM   #1
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2017 25' Flying Cloud
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Battery level fluctuating

We are first time boondocking with our new Zamp 230w portable and are puzzled by the fluctuating battery readings we see on our original equipment monitor panel. Last night, after disconnecting the solar, it read 12.5. It read the same this morning when we awoke and turned on the heater (propane). Very soon we saw a reading of 11.8 on the monitor! We turned off the heater and the monitor was once again showing 12.5 This happened several times over the course of the morning. What is happening? Are we damaging our lead-acid batteries? How do we know what the true condition/state of our batteries?
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Old 06-05-2020, 12:10 PM   #2
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No you are not damaging them. Lead acid have a number of chemical and physical induced characteristics that manifest as voltage variations that depend on load, level of charge, internal temperature, battery health and a number of others.

With no load and resting, the battery will show 12.3 to 12.8 depending on temperature when fully charged. When drawing current, voltage will be between 12.7 and 7.5 depending on how much current is being drawn, but batteries can only safely have high discharge rate for short periods, 30 seconds at most. So you never want to see your batteries under load showing less than 9.5 volts and you never want to see resting voltage less than 11.7, they will last longest if you never see the resting voltage less than 12.1. The degree of loss for a particular draw is a great way to asses overall health of the battery bank. For 11.8 volts that is about a 20 amp draw for a good group 24 battery. You have two so that would correspond to 40 amps which is 3 times what the furnace actually draws but this assumes a full charge which you did not have so 11.8 is a reasonable result.

Summary, assessing the health of batteries while in use is difficult. You are not damaging your batteries. Keep the resting voltage above 12.1 if you can and the load voltage above 10.

You can buy a battery load tester to asses battery health. Amazon sells several. I paid $40 for a decent one from Amazon. The Konnwei KW600. It is cheap and it is more accurate than I was expecting. Properly interpreting the results is difficult so if you go this route post a follow up and I'll explain it. If you have wet cells with cell caps you can test the health when fully charged using a hydrometer to compare acid specific gravity to ideal .
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Old 06-05-2020, 12:18 PM   #3
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This is very helpful and informative. Thank you very much!
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Old 06-05-2020, 12:54 PM   #4
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You're welcome, glad to help. I suppose I should have said you never want to see resting voltage below 11.5 accounting for lower northern and mountain temperatures and considering that boon docking sometimes you have no choice but to continue to use the battery even though you are being hard on them.

Happy camping. Be sure you use shore power from time to time to fully restore your batteries. It can take up to 12 hours at 14.6 or more volts to fully recover wet cells.
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Old 06-05-2020, 04:18 PM   #5
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Thanks, again 🙏 So grateful for this resource and the helpful, knowledgeable folks who help us newbies 🙂
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Old 06-05-2020, 05:54 PM   #6
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Good summaries, Brian.

The one minor detail I might add, Bob and Stella, when you want to read the battery voltage on the trailer's monitor panel, is to first let the batteries rest for an hour or so after charging from any source [shore power, tow vehicle, or solar panel].

FYI this Battery School is a good primer on RV batteries in general:

http://www.batteriesnorthwest.com/batteryschool.cfm

Be sure to read up on caring for the batteries, incl. water in flooded cell batteries, per the above source and your owner's manual.

You might also want to check out the Batteries etc. sub-forums for helpful topics:
https://www.airforums.com/forums/f37/
https://www.airforums.com/forums/f449/

For deep woods boondocking in cloudy weather you might consider a small generator running on propane off the trailer's quick-connect low pressure fitting at the front. We have a Yamaha 1000 watt gen for this. Other folks prefer Honda. We charge whenever the battery level gets below 12.3 if possible, depending on campground rules and the neighbors of course. The 1000 watt units are incredibly quiet and unobtrusive IMO. We also run the fridge on 120-volt AC when the gen is running. It won't however run the air conditioner.

"1000 watt gen Yamaha Honda" search results for this site:
https://www.google.com/search?q=1000...=airforums.com

Sometimes a small gen is the right tool for the small battery-charging job, and is also very useful at home for portable emergency power, running off a standard 20-lb. BBQ tank.

FYI here is the generator forum:
https://www.airforums.com/forums/f448/

Good luck.
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Old 06-06-2020, 10:48 AM   #7
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Hi Bob, all good advice here. One more thing to add, you mentioned that you turned on the "heater (propane)". If you mean "the furnace", the blower draws about 7 amperes and is probably the has the largest power draw of all the 12 volt appliances. For that reason unless it's below freezing out (the furnace ducts warm air to the holding tanks) we refrain from running the furnace at night. The voltage drop you saw was normal. As other said to really measure the battery you need to let it rest an hour or so and also measure at the battery itself. Along with my solar charging system and readout I added one of these on the battery which gives you bluetooth smartphone access to your batteries state of charge both instantaneously and historically. I leave my system up continuously (even in storage) and it's great to look back a week or month and see how the solar/battery are doing. https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1 Have fun out there! - Brad
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Old 06-06-2020, 10:55 AM   #8
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Here are a few images from the battery monitor app. You can see where I plugged the trailer into shore power on March 20.
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