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Open Roads Forum  >  Tech Issues

 > Battery Percentage Before Charging.

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1L243

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Posted: 03/16/21 08:05pm Link  |  Quote  |  Print  |  Notify Moderator

I was wondering what the consensus is on what your AT REST battery level of charge is before you feel you MUST get in on the charger? Understanding percentage may vary depending on type of batteries.


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Posted: 03/16/21 08:53pm Link  |  Quote  |  Print  |  Notify Moderator

12.2 volts is roughly 50% discharge. I don't like to go below that. At that point I am down 150 AH on my 300 AH bank so that means a lot of charging will be needed. Three hours of charging will only get me to about 90%.

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Posted: 03/16/21 09:00pm Link  |  Quote  |  Print  |  Notify Moderator

My idea is to use an electric toaster in the morning, so I need enough battery to run the inverter without it shutting off from low voltage.

So once you know your voltage drop from running the toaster, say 0.6v (you will have your own number), and knowing what the inverter's limit is (11v?) that means before you turn on the toaster, battery voltage must be at least 11.6 plus a bit, call it 12v. That happens to be about 40% SOC with mine.

Playing it that tight, you have to turn off the furnace first for a few minutes, so it does not come on and kick off the inverter before the toast is made. Later that morning, out comes the generator.


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Posted: 03/16/21 09:04pm Link  |  Quote  |  Print  |  Notify Moderator

While camping I recharge at 50% which takes about a week. At home when the batteries reach 80% I recharge.

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Posted: 03/16/21 09:09pm Link  |  Quote  |  Print  |  Notify Moderator

12.2 is not too soon to put a charge back in. 12.4 is OK to charge some depending on expected usage overnight or such.


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Posted: 03/17/21 08:24am Link  |  Quote  |  Print  |  Notify Moderator

Depends on how many cycles you want from your batteries. The deeper the discharges, the fewer the cycles. With a solar system your issue would be largely academic. Sun isn’t quite up yet but solar is giving my batteries some charge regardless of their SOC.


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Posted: 03/17/21 08:32am Link  |  Quote  |  Print  |  Notify Moderator

This way a shunt based battery meter is so much better than reading battery voltage. When I checked this morning I'm at 81% SOC. My voltage is 12.2.
My batteries started charging when the sun came up.


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BFL13

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Posted: 03/17/21 08:49am Link  |  Quote  |  Print  |  Notify Moderator

corvettekent wrote:

This way a shunt based battery meter is so much better than reading battery voltage. When I checked this morning I'm at 81% SOC. My voltage is 12.2.
My batteries started charging when the sun came up.


That is a warning sign that your AH counter needs to be zeroed (when the batts are truly full), or else the 12.2 was a loaded voltage at the time with the furnace running perhaps.

Cross-check the SOC from AH counter with the voltage before solar starts raising the voltage and when nothing much is on early in the morning (so close to resting as it gets when camping) regularly to see when the monitor's AH counter is getting out of whack.

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Posted: 03/17/21 01:06pm Link  |  Quote  |  Print  |  Notify Moderator

My Trailer is in covered storage so no sunlight for the panels.

I'm in the process of watching my shunted battery monitor slowly come down from the little parasitic loads inside the trailer. at a 0.01 percent draw it might take a while.

I'm doing this on purpose so I can get a understanding on the accuracy of the battery monitor. It's been about 10 days now and the battery is currently showing 12.5 volts at 97% capacity. I set the monitor after charging fully then resting for 4 hours at 100%

The monitor can be set at 100% if fully charged or at 0% if dead. Not wanting to discharge my batteries fully I chose the 100%. But I did read somewhere that setting at 0% percent then letting the batteries find 100% when fully charged might be a more accurate setting?????

I'm thinking 12.2 volt will be as low as I will go with the test. Under normal circumstances I usually don't go below 12.3 volts

BFL13

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Posted: 03/17/21 01:38pm Link  |  Quote  |  Print  |  Notify Moderator

Drawing them down slowly means that whole time they are below full they are sulphating. Sulphation hardens over time so it becomes more difficult to desulphate and after a longer time impossible.

IMO do the test with a higher amp load and get it all done in less time, so you can recharge sooner.

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