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Old 11-24-2020, 09:12 PM   #1
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Battery Voltage - How Low ???

I have a 2021 Dutch Star and am using more Harvest Host locations than I thought (boondocking). Although many locations donít mind if you run the generator, these are businesses and Iím trying to be considerate. The battery voltage starts at 13.6V...I watch a TV with DirecTV dish, and of course the residential fridge. Iíve only had this coach for 1 month, and not sure low low I should let the battery voltage drop before I start the generator. It seems I can live about 6-8 hours until the voltage drops to 12.4. I do not have the Inverter setup to automatically start the generator. So my question is how low can I let the battery voltage drop before i start the generator. This is only a short term problem as I have an appointment to get a full solar system, lithium batteries and inverter installed in January. Thanks.
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Old 11-24-2020, 09:22 PM   #2
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I would not let the batteries drop below 50% state of charge which is 12.2 on a 12 volt system.
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Old 11-24-2020, 09:24 PM   #3
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If the batteries only need to last until January, you can truly deep cycle them.

You can run them down to 11.8 volts, 500 times from brand new, so you can start recharging from there and see what happens.

Get your AHs out of them before you swap them out.
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Old 11-24-2020, 09:29 PM   #4
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If the batteries only need to last until January, you can truly deep cycle them.

You can run them down to 11.8 volts, 500 times from brand new, so you can start recharging from there and see what happens.

Get your AHs out of them before you swap them out.
Yes that makes sense since you are changing them out so soon. Use them like you stole them
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Old 11-24-2020, 09:30 PM   #5
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Here is a chart showing depth of discharge compared to cycle life for Lifeline batteries. Its comparable to most deep cycle batteries.

The 50% suggestion is a compromise between cycles and longivity. There will be no harm in running them down to 20% state of charge.Click image for larger version

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Old 11-24-2020, 09:46 PM   #6
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Quote:
Originally Posted by twinboat View Post
If the batteries only need to last until January, you can truly deep cycle them.

You can run them down to 11.8 volts, 500 times from brand new, so you can start recharging from there and see what happens.

Get your AHs out of them before you swap them out.


Thanks for your good input, I really appreciate it.
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Old 11-24-2020, 09:50 PM   #7
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Battery Voltage - How Low ???

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Yes that makes sense since you are changing them out so soon. Use them like you stole them


Taking it out for the next 10 days (all Harvest Host locations with no power). I will run them down a little more and see how long they last. I appreciate your input.
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Old 11-24-2020, 10:08 PM   #8
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Originally Posted by twinboat View Post
Here is a chart showing depth of discharge compared to cycle life for Lifeline batteries. Its comparable to most deep cycle batteries.

The 50% suggestion is a compromise between cycles and longivity. There will be no harm in running them down to 20% state of charge.Attachment 309195Attachment 309196

A follow on tip to Twinboat's info. Contacting your specific battery manufacturers and asking them for two sets of numbers: 1) Battery At Rest - Voltage to SOC; 2) Battery Under Load - Voltage to SOC.

The majority of the time when we really want to know the relative SOC level of a battery bank, we're 'Under Load' conditions. Very seldom, well at least for me, do ever shut down the demands on the battery bank long enough while using the RV, to get an accurate 'Resting' battery bank voltage...

For those who have SOC monitoring capabilities, not as important. But for those who only have Battery Voltage monitoring - knowing the Under Load values is important.

Best to all,
Smitty
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Old 11-25-2020, 06:58 AM   #9
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The depth of discharge in the previous chart was probably if you measure the batteries, completely free of any load...and after a resting period to allow surface voltage to dissipate.

This chart allows you to estimate the voltage as it changes under load.

You divide your bank capacity... ie my 928aH banks C/100 load would be 9.28 amps... and so in.

I do agree that 12.2 is a good target...and if you are planning in new batteries soon...discharging them more, if needed,,,like Twinboat suggested is a good plan too.
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Old 11-25-2020, 07:18 AM   #10
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completely free of any load...and after a resting period to allow surface voltage to dissipate.

.
During discharge, you would wait for the voltage to spring back, not for surface voltage to dissipate.
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Old 11-25-2020, 07:48 AM   #11
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Hi - Keep in mind that if these boon docking stays are back to back you need enough time to recharge the batteries. More out means longer to recharge. Your engine alternator is meant to keep batteries charged, not to recharge depleted batteries. It's all a balancing act.


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Old 11-25-2020, 08:49 AM   #12
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Run 'em like a rented mule, they're getting recycled soon. There's no reason you can't run them to just above the point the generator won't start. What that point is you'd have to find out by trial and error but since you're here, no reason not to treat this as an opportunity to find out where that point is. During one of my capacity tests I did this, and my generator started with the battery below 11V so I was pretty happy about that.

Good responses so far mentioning the difference between static voltage, and voltage under load. 10.5V is the minimum voltage you want to run them down to under any current level. Practically speaking your loads will quit working at and below this voltage level, so it's a good stopping point for numerous reasons.

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