Boondocking - do my batteries need to be replaced?

Alfa38User said:

It takes many hours (ie up to 24 or more hours) to charge a discharged battery or batteries fully, several hours barely start it. For the Marine/RV type of battery, discharging them much more than 50% will quickly ruin them and result in a much shorter life.

The charge condition display, often found on a tank display unit, will always show full charge (5 lights) when plugged in or when the engine or generator is running on a motorized camper as they are reading the charger (alternator/converter) output (usually about 13.5 volts or better).

Click to expand...

But, it reads fully charged when not plugged in and when not operating the generator.  My rooftop solar cell generally maintains the charge pretty well, so I don't think I have been storing it at half charge very often.  If these are original batteries I have no complaint with the life.

The voltage doesn't really tell you how many amp-hours are available.  A battery can be "fully charged" and still have almost no amp-hours of power available to use. A group 27 deep cycle will have a amp-hour capacity of about 110 when brand new, but it deteriorates steadily as it is discharged and recharged. Marine/RV hybrids like the SRM-27  are good for maybe 150 deep  (more than 50%) discharges over their life span. They last longer if rarely deep discharged, and hardly any time at all if frequently deep discharged. Other factors affect life and capacity as well.

A load test will give some indication of how much amp-hour capacity remains. Not a real number, but at least it is measuring amps rather than volts.

If the battery is always on charge and never cycled at all it could be suffering from stratification/sulfation.

Yeap, that's one of the several ways a battery loses its capacity to store much power.

Gary RV_Wizard said:

Odds are the battery(s) are just plain worn out. The typical marine/RV so-called deep cycle has a service life of about 3 years, and the capacity deteriorates badly toward the end of that.  If they are a better quality deep cycle, e.g gold cart 6v's, you could expect 5-10 years with decent care, but even so the battery in a 2010 coach would probably be near end of life.

Since you rarely camp off-grid, I'd probably get another marine/rv type for a modest price. However, you might want to review my article on RV Battery Choices in the RVforum Library at http://www.rvforum.net/miscfiles/Choosing_right_battery.pdf

Click to expand...

Today I finally had time to do something about this.  While I would like to have Trojans like I put into my golf cart, Gary is right when he said I am rarely camping out of a campground, so I went to Costco with both of my Interstate batteries to get a replacement.  Costco here is only selling Interstates, which is what I was replacing.  Costco does not test batteries like they do at Sears or other places. And, even if they did I am not sure it would tell me definitively if they were toast.  That said, I am convinced that these were the original batteries based upon what I know about the original owner,  who only put 6800 miles on this coach.  If so, 6.5 years is more than good enough. 

Trojan's  AG-27 on Amazon is prices at $275, not including $47 more in shipping.  Perhaps they are less elsewhere.  When I looked at Costco's Size 27 Interstate two of these only cost me $146, which put then at 1/4 the price of the Trojan.  I can buy a lot of replacements for that price so I bought 2 and installed them this afternoon.  These are rated at 600 CCA, which is a very strange way to rate a deep cycle battery, but i assume they are just like the 750 MCA batteries I am replacing which should be good enough. Now I need to look into a better gage for charge levels since mine always reads fully charged.

Apples & oranges!  You are comparing Trojan AGM deep cycle battery (the AG-27) to a flooded cell Interstate, so hardly surprising there is a big price difference. An AGM is typically 50%-75% more than a flooded cell type of the same size.  I'm guessing the Interstate was another SRM-27?  That model is rated for 600 CCA, though CCA is irrelevant for a deep cycle. 

Ought to work adequately for you, but don't be surprised if it gets low on capacity in 3-4 years.

Yes, I know it is not a fair comparison, but that was the option was considering instead.  If these do as well as my last equivalent batteries I will be delighted.  Or, at this price I will buy 2 more in 3-4 years. Why a manufacturer would rate a deep cycle battery with a CCA number is beyond me, but they  have now dropped the other rating number from their product.

That battery is probably a dual purpose marine battery, not a true deep cycle. That's why it would have a CCA rating.

JoelP said:

I invited my daughter and her family from to spend the night in my RV while the smoke is so heavy from the fires just north of them. I parked where I couldn't easily plug in but only ran 2 fans for 3 hours and then one LED light and one Fantastic fan.  To my knowledge nothing else was drawing current. The 2  coach batteries died by the time that 15 hours had elapsed.  All would have been OK except that the depleted battery set off the CO detector at 3:00AM.  I had to start the engine to be able to start the generator, which stopped the CO detector from sounding of.

I have a solar panel on the roof that keeps this battery charge maintained during storage.  Occasionally I check the fluid in the cells and they never seems to need any water.  As for the age of these batteries, I am unsure since they came with the vehicle from the prior owner.

Normally I only used this when plugged in at a campground, so I have little experience with what to expect.  What is reasonable to expect when boondocking like this for that small amount of electrical load?

Click to expand...

Inasmuch as you inherited those batteries it's possible the previous owner didn't take care of the batteries well and they've been lost to sulfation. Or, they're just old. In either case, you will replace. The other thing is that solar chargers are not the end-all and be-all of battery solutions, IMHO.  When left alone for long periods of time, it's almost mandatory to keep batteries in a full charge condition. Solar chargers are dependant on sun, of course, so the amount of voltage/amperage going into the battery at any given time is variable, especially in the winter months, not to mention day and night time. You might check to see how much voltage the solar charged generates in good and bad weather. You need at least 14-15 volts coming into the battery for it to be charging well.

The best way to keep a battery in tip top shape is to keep it on a drip charger like a Battery Tender. For 25 bucks it's great insurance.

I learned this the hard way, when I used to leave my motorcycle batteries sit for long periods in the off-riding season. What happens is that sulfation sets it and the capacity of the battery to hold a decent charge is gradually diminished. (I think of it like siltation in a dam. After years the amount of water dams hold back lessens due to silt washing into the reservoir.) the only way to avoid it is to keep the battery fully charged as much as possible. I get three-four years out my ordinary lead/acid moto batteries now.  I'm not sure trusting it to sunlight is the way to go.

Just my opinion.

flylooper said:

...The other thing is that solar chargers are not the end-all and be-all of battery solutions, IMHO.  When left alone for long periods of time, it's almost mandatory to keep batteries in a full charge condition. Solar chargers are dependant on sun, of course, so the amount of voltage/amperage going into the battery at any given time is variable, especially in the winter months, not to mention day and night time. You might check to see how much voltage the solar charged generates in good and bad weather. You need at least 14-15 volts coming into the battery for it to be charging well. ...

Click to expand...

All good points. I  don't have a very large solar charger, but I do live in Northern California where we get mucho sun.  I will try to put a meter on this and see how much current it is delivering in various conditions.

It isn't just the longevity of the true deep cycle but the storage capacity as well. Most RV-Marine batteries have 80-90AH while a pair of Trojan T-105s have 225AH.

Jeff said:

It isn't just the longevity of the true deep cycle but the storage capacity as well. Most RV-Marine batteries have 80-90AH while a pair of Trojan T-105s have 225AH.

Click to expand...

Yes, well understood. If I find the occasional one night of fan and LEDs lights experience cannot make it through with 80-90 AH I will purchase the Trojans next time.

For all of us with RV's and multiple vehicles I think having a battery load tester is a must. The one I have is a simple idiot proof, no digital crap to figure out how to make work. It's similar to this Harbor Feight unit;  https://www.harborfreight.com/100-amp-612v-battery-load-tester-61747.html
It tells me in 10 seconds what would take me an hour otherwise. Removing the battery, lugging the thing to & from the car/RV, having the snot nosed kid at O'Reilly's fiddle around with their digital tester to tell me "it's bad". I don't want to believe him...just sayin'.

99dart said:

For all of us with RV's and multiple vehicles I think having a battery load tester is a must. The one I have is a simple idiot proof, no digital crap to figure out how to make work. It's similar to this Harbor Feight unit;  https://www.harborfreight.com/100-amp-612v-battery-load-tester-61747.html
It tells me in 10 seconds what would take me an hour otherwise. Removing the battery, lugging the thing to & from the car/RV, having the snot nosed kid at O'Reilly's fiddle around with their digital tester to tell me "it's bad". I don't want to believe him...just sayin'.

Click to expand...

Are you saying that you use this load tester without disconnecting your batteries?  Do you test a pair of batteries still hooked up in parallel and hooked to the RV?

Yes, you can load test while the batteries are connected, as long as shore power is disconnect or the breaker for the converter/charger is shut off (batteries not being charged). And yes, you can test the two 6v's as a pair - they become one 12v battery when wired in series.

Gary RV_Wizard said:

Yes, you can load test while the batteries are connected, as long as shore power is disconnect or the breaker for the converter/charger is shut off (batteries not being charged). And yes, you can test the two 6v's as a pair - they become one 12v battery when wired in series.

Click to expand...

And, I assume the same is true for 2 12V in parallel.

JoelP said:

And, I assume the same is true for 2 12V in parallel.

Click to expand...

You would want to separate them. You can test a bank of two sixes as a 12 but if you get a low reading you then need to separate them to see which one is bad. Not that you wouldn't probably replace both. The issue with load testing is that it does no good unless the battery is charged. You can load test a perfectly good battery and get a low reading if the charge is low. Where I have found a load tester to be most effective is when the load is applied and it drops very low very fast and it usually indicates at least one bad cell. You will also see that if you check the Specific gravity. If you take a discharged battery into some auto stores and they test it and it drops low they will say the battery is no good when it may just need a charge or eq. If you cant get it to take a charge it's junk before they even load test it.

If you attempt to fully charge and still see low SG you can then try to equalize. If the SG wont come up after equalizing you can attempt to eq again or higher voltage to drive it up while watching that the bubbles only happen every second or so. It shouldn't be rapidly bubbling. If the battery then seems to work better but just cant keep up as it used to it's junk.  At that point you are just spending time to nurse it along.

JoelP said:

Are you saying that you use this load tester without disconnecting your batteries?  Do you test a pair of batteries still hooked up in parallel and hooked to the RV?

Click to expand...

Up to this point I have never had an RV with multiple batteries. So, I have tested just single batteries from vehicles with single batteries.
Gary rv wizard stepped in with good info as always! 

99dart said:

Up to this point I have never had an RV with multiple batteries. So, I have tested just single batteries from vehicles with single batteries.
Gary rv wizard stepped in with good info as always!

Click to expand...

Yep,a single battery is a single battery. So even if you have 3 or 4 or more 12's in parallel you need to separate them to test them otherwise you are just testing the bank. When disconnected from parallel and checking, one could be bad and drag the other down so attempt to charge both while separate and re test.

IIRC you are testing the load across the terminals you are connected to, not the bank.