battery questions

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TrvlShell

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Jan 17, 2016
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We're new to RV-ing (we have a small travel trailer which we've taken on three trips so far).  We dry camped for the first time on our last trip, and had some battery issues.  The RV and battery are new.  We were fine the first night.  Our friend lent us his generator and on the second day, we charged the battery via the generator.  The battery display seemed to read full when we unplugged the generator, and we tried to be very cautions with battery usage (just turned on a couple of lights for about 10 minutes plus ran the water pump briefly).  However, the battery didn't last through the night.  In the middle of the night, noticed the fridge (which was running on propane) light was red (which we believe means not enough power to run the control board of fridge).  And then at about 5am, the propone/CO detector started beeping (which we believe meant no power to it).  Another night we tried charging the battery via the generator as late in the day as possible (we turned it off just before quiet hours started), and didn't use any "extra" battery power - no lights, no water pump, etc.  So it was just what the fridge, detectors, etc. needed.  And the battery still didn't last through night.

We know we have a small battery, and it wasn't going to last long, but we would expect it to at least be able to make to through the night (especially with limited power use).

Did we just not charge the battery long enough with the generator (even though it looked like it showed fully charged)?
How long should it take to fully charge the battery with a generator?
We were camping with my brother-in-law, who has a pop-up.  They also have a group 24 battery, and used their lights (and often a had a fan running as well) much more than we did, and their battery lasted over three days.  Why so much difference?  Can there be that much difference in amp hours between two different group 24 batteries?
Is there a chance that there is something else drawing power from the battery that we're not aware of, and if so, what could that be?

Thanks!
 

kportra

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You will get a lot of good answers and information here.  I'm not a techie - so I will start with some basic things.  We bought a trailer new off the lot last year and added a battery and had problems all summer.  Turns out the battery that came with our trailer was a dud.  So my first advice would be to take it to a battery store (Batteries Plus is where we went) to have it charged up and tested.

When charging a battery with the generator, your dumb display will show fully charged.  If you wait about 1/2 hour after taking the charge off and maybe run a couple things (water pump, lights on), then look at the reading it will be more real.

The last thing we learned last summer is that it takes a long, long time to charge a very low battery.  I'm talking hours and hours.  Not knowing your amp/hours or about your converter I can't give you a firm number, but an example would be for a 74 amp/hour battery 50% discharged and a low end converter that allows a charge at 3 amps per hour - it could take 12 hours to charge.

So - our solutions were to replace the bad battery and to add a 100 watt portable solar panel to our power management.  Hubby has a CPAP that runs off the batteries at night, so we probably use quite a bit more power than you.  We've had much more relaxing trips after those two changes.

Good luck.
 

Back2PA

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kportra said:
So my first advice would be to take it to a battery store (Batteries Plus is where we went) to have it charged up and tested.

When charging a battery with the generator, your dumb display will show fully charged.  If you wait about 1/2 hour after taking the charge off and maybe run a couple things (water pump, lights on), then look at the reading it will be more real.

Good answers. Don't know if you have a digital battery readout or one that reads in bars showing percent full. If bars, those are essentially useless so you'll want to add a digital readout. To add some detail, once you've turn off the charger and waited, you can also use a voltmeter at the battery. As you can see from the attached chart a fully charged 12V battery should read 12.6-12.7 volts to be fully charged. (If it reads more than 12.7V that is the leftover "surface charge" and it not a true reading. Run a light for 5 minutes then try again.) Since, to avoid life shortening damage you shouldn't discharge your battery below 50%, the minimum voltage is around 12, which is the irony of calling it a 12V battery - at 12V it's actually already "dead" from a use standpoint. Will the lights still come on or pump run? Yes, but below 12V and you are harming your battery long term.

So the advice to get your battery checked is good. My guess is that the battery wasn't fully charged when you went to bed.
 

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John From Detroit

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FIrst some numbers. These are C/20 or capacity in amp hours discharged over 20 hours.

Group 24 about 75
Groups 27/29 just under/over 100
Group 31.  about 130
These are USUALLY MARINE/deep cycle not true DEEP CYCLE so you can only use about 20-25% of the capacity before damage sets in fast.

GC-2  220 amp hours. Now these are SIX volt but two in series makes a big 12 volt (Still 220 amp hours) and GOLF CAR (GC) batteries are DEEP CYCLE. meaning you can use half befor serious damage sets in.

Now.  Charging.
Assuming you have a good 3 stage charge with a capacity of about 1/3 the C/20 rating (IE: [email protected] of 220 is 66 amps) six hours to recharge. NOTE. Double the battery bank you only add about 2 hours.


One other thing.. When charging and for at least 15 minutes after the display will read FULL even though the batteries may be far from it.. Nature of how it works.
 

TrvlShell

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Jan 17, 2016
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Sorry I didn't get a chance to come back and respond sooner, but wanted to thank everyone for the responses - they were very helpful!  And Sun2Retire, thank you for the battery charge/voltage chart - I've saved a copy to my RV notes.

I think we're going to get our battery tested just in case, but it sounds like we just didn't run the generator long enough to charge the battery.  We're dry camping again next week, so hopefully we'ill do a better job at the battery management.

My husband ran a test to see how long the battery would last with just the refridgerator on (running on propane).  After about 24 hours, the battery was at about 50%.  Does this seem right for a group 24 battery?

Thanks again!





 

Gary RV_Wizard

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My husband ran a test to see how long the battery would last with just the refridgerator on (running on propane).  After about 24 hours, the battery was at about 50%.  Does this seem right for a group 24 battery?
For a new Group 24 12v, that says you used about 40 amp-hours in 24 hours or about 1.6 AH/hour. That's much more than any LP fridge circuit board should consume, so I suggest you have other loads you aren't aware of. Maybe the fridge has a anti-condensation heater? Or something else in the RV, e.g. the LP gas detector or a CO detector? They all add up.

If not a new battery, it seems likely it is well into its life cycle and the fridge load (maybe 10-12 AH over 24 hours) is enough to drag it down to the 50% level. 
 

TrvlShell

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Jan 17, 2016
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Thanks John, Gary! 

Well the battery was supposed to be new (the RV is new) but I guess we can't really know for sure.  My husband took the battery and had it tested and it came back as bad.  So he took it back to the dealer, they said it tested good, but gave us a new battery anyway.  So now we have a (hopefully) new battery.  We're dry camping again next week so we'll see how this one does.  We're going to watch the battery more closely this time so hopefully we'll be able to do a better job at battery management.

Our fridge is a Norcold.  Not quite sure about the "anti-condensation heater" heater, but I will look into that.  Would that be the type of thing that would run on battery when the fridge was running on propane?  We do have LP and CO detectors which I know also use the battery, though I thought they didn't use much.  The smoke detector has a battery, but not sure if it also uses the trailer battery.  Can't think of anything else that would have been using the battery.


John From Detroit said:
Seems good for a group 24 but unless it is a DEEP CYCLE (not a MARINE/deep cycle) running it that lwo is ... not a good idea.
I thought I had read that it wasn't good to let the battery go below 50%, but I thought letting it get down to 50% would be okay.  Is that not the case?  What % charge should we be trying to keep the battery above?

 

Optimistic Paranoid

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TrvlShell said:
I thought I had read that it wasn't good to let the battery go below 50%, but I thought letting it get down to 50% would be okay.  Is that not the case?  What % charge should we be trying to keep the battery above?

Well, you start with a fully charged battery, and various things run off it for a while - lights, a fan, your RV water pump, maybe you recharge your laptop, etc.  Then you charge it back up to fully charged.  That's one CYCLE.  Now, your battery is going to contain a certain amount of available electrical power, usually expressed as amp hours.  If your battery contains 100 amp hours, and you use 50 amp hours before recharging it, that's a 50% cycle.  If you only used 30 amp hours before recharging, your battery would still retain 70% of it's power, and that would be called a 70% cycle.

Now, a TRUE deep cycle battery, like a golf cart battery, or the ones used if industrial floor sweepers and such, will usually be good for 1,000 to 1,200 cycles at 50%.  If you used 70% cycles, you might get 2,000 cycles out of them.  If you regularly drained them down to 30% before recharging, you might get only a couple of hundred cycles out of them.  Trojan batteries actually have graphs available showing the expected lifespan in cycles vs the % of discharge.

So basically, we are talking about battery longevity here.

BTW, the so called marine-rv "deep cycle" batteries are actually hybrid batteries that fall somewhere between TRUE deep cycles and car starting batteries.  They were originally designed for use on boats, where it was necessary to leave various anchor and running lights on overnight, and still be able to start the boat next morning.  On a 50% cycle, they are usually good for about 400 cycles before they die.

Car starting batteries, under normal circumstances, never go below 95%.  Once the engine starts, the alternator supplies all the power to the electrical system.  If you ran them down to 50%, you'd be lucky to get 40 to 50 cycles before you killed them.
 

Gary RV_Wizard

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Not quite sure about the "anti-condensation heater" heater, but I will look into that.  Would that be the type of thing that would run on battery when the fridge was running on propane?
Yes, if you have that feature it runs all the time the fridge is on.  Some fridges have a switch for it, but not many of the newer ones do.  It's purpose is to keep the outer skin of the fridge dry by warming it enough that moisture doesn't collect on the surface (cold surfaces collect moisture).  It's not a lot of current draw, but every little bit hurts when camping without shore power and very limited battery capacity.
 

mel s

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Apr 28, 2014
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TrvlShell said:
I thought I had read that it wasn't good to let the battery go below 50%, but I thought letting it get down to 50% would be okay.  Is that not the case?  What % charge should we be trying to keep the battery above?

TrvlShell
The SoC, (State of Charge), of a 12V "flooded lead acid battery" is 50% at 12.06 volts
See: http://www.rvtechlibrary.com/images/voltchart.gif
     
 

ChasA

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Mar 21, 2009
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2,325
Mel, check the chart again.  12.6v is 100% 12.06v is 50%. Maybe time for an eye exam.
 

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