# Deep cycle RV/marine battery charging



## Pydpiper (Jun 21, 2006)

I just bought a new deep cycle battery, I also have one about 1 year old..
I am going camping this weekend and I only get one shot at charging this thing right, it is at full voltage right now (12.75v) and it will run the lights inside the camper for three days, I hope.. I will have no way to recharge this battery should it die..
-Would it be wise to charge it more prior to leaving?
-Should it run simple 12v lights for a couple days?
-Is 2 amps a good charge voltage? Its as low as my battery charger goes.

Any tips on how to maximize it's life over the weekend?


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## Ras_Thavas (Jun 21, 2006)

I would put it on a maintenance charger overnight. Those generally charge at less than 1 amp. You would have to get exact figures from the battery manufacturer, but I would suspect that the voltage when the battery is at capacity will be in the high 13's.

To figure out how long you can run something you need to know how many amp the device will use and the capacity of the battery in amps.

For instance, I have a deep cycle battery that has a 55amp capacity. If my device draws one amp then I can power it for approximately 55 hours. This is not taking into account any losses due to ineffeciance of wiring and connections, and the fact that the battery may not be able to deliver full voltage as it gets lower in capacity.


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## Brighteyez (Jun 21, 2006)

What kind of camper is this? If it's a trailer or a pickup camper, there should be a charging circuit to the battery from the vehicle's alternator and you would also be charging the battery in the camper as you drive. If your charger is a 10/2A charger, you can charge it at 10A and then drop it to 2 to keep a trickle charge on it until you leave.



Pydpiper said:


> I just bought a new deep cycle battery, I also have one about 1 year old..
> I am going camping this weekend and I only get one shot at charging this thing right, it is at full voltage right now (12.75v) and it will run the lights inside the camper for three days, I hope.. I will have no way to recharge this battery should it die..
> -Would it be wise to charge it more prior to leaving?
> -Should it run simple 12v lights for a couple days?
> ...


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## Pydpiper (Jun 21, 2006)

It's a travel trailer, but far from new.. It does not connect to the tow vehicle through a 12v supply, my truck supplies it but the trailer does not have the resources. Also, I do not believe the trailer is capable of charging the battery when it is plugged in, the inverter allows me to choose between battery supply or 110, while on 110 I have no power coming back to the battery, unless I have done something wrong, but it seems pretty simple..

So I can charge a deep cycle at 10A?

This battery claims to be 120 Amp hours..


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## Brighteyez (Jun 21, 2006)

I'm familiar with the DC power supply that you're referring to, no, it does not charge the battery when it is connected to AC. You would need to carry a charger with you and connect that to an AC outlet.

Every travel trailer (at least in the last 25 years or so) has a 12V line to the pigtail. If you added the battery on your own, I suppose you could have neglected to connect that line to the battery. But I'm sure it's there and all you would need to do is connect it to the battery terminal (it might be connected to the 'battery' terminal of the trailer's power converter as well, just connect it to the battery and run another line from the battery to the converter.)

First of all, those batteries are not true deep cycle batteries, they're only slightly better than a car battery for repeated discharges. Yes, you can charge it at 10A, and you should recharge as soon as you can after usage, avoid repeated full discharges, and keep it fully charged as frequently as possible (at least once a quarter, once a month would be nice.)

120 Amps? Must be a Size 27 battery, the 24s are generally rated for less. 



Pydpiper said:


> It's a travel trailer, but far from new.. It does not connect to the tow vehicle through a 12v supply, my truck supplies it but the trailer does not have the resources. Also, I do not believe the trailer is capable of charging the battery when it is plugged in, the inverter allows me to choose between battery supply or 110, while on 110 I have no power coming back to the battery, unless I have done something wrong, but it seems pretty simple..
> 
> So I can charge a deep cycle at 10A?
> 
> This battery claims to be 120 Amp hours..


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## Illum (Jun 21, 2006)

Pydpiper said:


> ....it is at full voltage right now (12.75v) and .....



My measurements on my deep cycle gel cell from exide [18 AH] measures 13.9V on a full charge

Interesting, either my battery is newer or my meter needs to retire


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## Diesel_Bomber (Jun 21, 2006)

Brighteyez said:


> First of all, those batteries are not true deep cycle batteries, they're only slightly better than a car battery for repeated discharges.



I take issue with this statement. True, most so called "deep cycle" batteries are little more than SLI batteries. Also true that this is likely what Pydpiper has, but it's entirely possible he has a good Rolls, Surrete, or Trojan deep cycle. Quick test: if there's any kind of cranking amps(CA, CCA, MCA) listed, it's not a real deep cycle.

Assuming it's a true deep cycle, you still don't want to go any farther than 80% depth of discharge, and 50% would be even better for maximum battery life. Most auto parts stores sell a battery maintainer which will keep your battery in tip top condition. Be warned that you have to add water while your battery is on a maintainer just like you do when it's in use. That's another point, if you can't add water then it's very likely not a true deep cycle. For manual charging a lead acid battery, I'd use 13.8v as hot off the charger voltage and 12.78v as full charge after the acid has equalized.



Cheers. :buddies:


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## Pydpiper (Jun 21, 2006)

Both of my batteries are Energizer brand.. And both list cranking amps... So, this means my battery is not a true deep cycle? Great.. I can smell the money burning already.. I bought it from Wall-Mart, so it can go back  .


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## Pydpiper (Jun 21, 2006)

Thanks for all the info guys.. I can see this is going to go down the road of no financial return, so be easy on me..
I bought this camper for the sole purpose of a mid September swap meet (second largest on the planet), it sits for 6 days in the middle of nowhere and houses my wife and kids without hydro or water supplies.. This coming weekend I can get by, but if there is bigger and better batteries out there I will leave the generator at home..

www.burlscreek.com

This weekend the camper will be on a beach, I just need to be sure I can keep some lights on...


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## TedTheLed (Jun 21, 2006)

to measure a 12 volt lead acid battery it should be under no load, and off of the charging source for at least 2 hours, a full new battery will be about 12.7 volts, a somewhat used one around 12.6 volts, after a couple/few years use 12.5 is good..

a 12 volt lead acid battery should not read 13.9 volts unless it is being charged.. 

the maximum charge rate should be about 20% of the battery capacity; for a 120 amp battery that would be 24 amps maximum, but watch yer water level.

remember; 100 amps of capacity at 12 volts = 10 amps of capacity at 120 volts -- which is 'only' about 1200 watt hours..minus 10% to 20% for line losses and losses going into then out of the battery.. that's why it's better to to use your electric devices while the sun is shining on your solar panels; you use the energy straight off the panels instead going into then out of the battery = less stress on the battery and more efficient use of the solar panel output.

of course if you need lighting at night, you need to use the batteries.. 12 volt DC fluorescent is most efficient. Using an inverter for 120 volts AC fluorescent is second best. 
...got solar panels?


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## Pydpiper (Jun 21, 2006)

Illum_the_nation said:


> My measurements on my deep cycle gel cell from exide [18 AH] measures 13.9V on a full charge
> 
> Interesting, either my battery is newer or my meter needs to retire




By "full voltage" I meant the voltage when it hit my workbench after getting home from the store.. My mistake, I haven't tried to charge it yet..


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## Pydpiper (Jun 21, 2006)

Ted.. How big of panels would I need? I was glancing at three models today.. They seemed to be more of a "maintainer" than charger.. I am not in the camper during the day, hardly ever, so my goal is to keep a good strong battery ready for sundown..
I like the thoughts of solar.. but of course it comes at a cost, today I seen everything from $39 to $99..
Tell me more..


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## Brighteyez (Jun 21, 2006)

All you had to do was mention the brand. I could have told you where you bought it . The plates are supposed to be a little thicker than a car battery and will take a bit more abuse, and they are marketed for use in RVs but it's not a true deep cycle battery. First of all you won't generally find deep cycle batteries in auto supply stores, secondly they cost enough to scare people away from them, and they tend to weigh a bit more than the deep cycle batteries that you find in automotive stores.

For your usage it should be fine, no need to go throwing money away because someone on a web forum starts posting snooty stuff about how a particular battery is the only one that is suitable (in their "opinion")

If it's one of the Size 27 Marine/Deep Cycle batteries, it will be suitable for use in your trailer. After all, it's not as if you're going to live in the trailer for months at a time where the battery is your sole source of electricity.

If you're going to be out for six days, just use one battery and bring the generator. Especially when the family is with you, they don't always understand that battery power is finite. Having a generator just makes things more conveient and at those swap meets and flea markets, the people in trailers usually have a portable generator for power anyway. Buying two batteries with the expection of running them both down and not recharging them until you get home is not good and you may very well end up with disposable batteries if they're left alone too long after being discharged.



Pydpiper said:


> Both of my batteries are Energizer brand.. And both list cranking amps... So, this means my battery is not a true deep cycle? Great.. I can smell the money burning already.. I bought it from Wall-Mart, so it can go back  .


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## TedTheLed (Jun 21, 2006)

you can get a 50 watt panel for around $300 a 75 watt for $400, maybe less. so figure if the sun shines for 6 hours on the 50 watt panel the math says that's 300 watts for an hour you just put in the battery (actually figure a little less for above-mentioned reasons) so you would be able to run a couple 10 watt fluorescents for a good 12 hours or so on the day's input..


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## Brighteyez (Jun 21, 2006)

The panels that will provide adequate current for charging will be in the thosands of dollars. I don't think those low cost panels will be adequate to replenish what you use each day, and the cost of gas to run the generator will be much less than the cost of solar panels for something that you probably won't be using that often.

*EDIT: *Maybe Ted has more updated pricing or perhaps the price has gone down considerably in recent years. The last time that I checked on a Siemens/Arco system for a motorhome it was almost $3,000. If there are more efficient panels available at a lower cost, it might be worth exploring.



Pydpiper said:


> Ted.. How big of panels would I need? I was glancing at three models today.. They seemed to be more of a "maintainer" than charger.. I am not in the camper during the day, hardly ever, so my goal is to keep a good strong battery ready for sundown..
> I like the thoughts of solar.. but of course it comes at a cost, today I seen everything from $39 to $99..
> Tell me more..


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## snakebite (Jun 21, 2006)

post a pic.
the energizer deep cycle i got in a camper last year was made by johnson controls.
had thick plates too.
the marine starting types are just a car starting battery with marine terminals.
real deep cycle batts are
1 very heavy
2 rated in amp hours
3 have few but thick plates.
4 must be slow charged.


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## Brock (Jun 21, 2006)

Diesel_Bomber said:


> if you can't add water then it's very likely not a true deep cycle.


I take issue with this statement  since I have 24kw of sealed AGM batteries, 12v at almost 2000 amps. I can assure you they are true deep cycle. They are eight Deka 8A8D AGM as seen here





But I agree that I'd use 13.8v as hot off the charger voltage and 12.78v as full charge after the acid has equalized. I absorb at 14.4v (lower since they are AGM) and float at 13.4v.

You can easily charge a 120a battery at 10 amps, the trick is what the voltage is while charging. Most chargers are “dumb”, even a cheaper 2 stage charger will work for this battery. I would recommend a small Deltran 800mA type charger, I use them on our cars and plug them in once a week in winter to top them off. You could use a charger like this and just leave it on the batteries when ever AC is available to keep it topped off, it would take a while to recharge it, but with no effort on your part.

Check out this forum for tips on batteries and solar charging for trailers and RV use. This thread has more loads but is a good start
http://www.wind-sun.com/smf/index.php?topic=1588.0


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## Brighteyez (Jun 21, 2006)

I would agree, I think that statement is gibberish. But why did you attribute it to me? That wasn't in any of my postings, and I really do know better than that 



Brighteyez said:


> if you can't add water then it's very likely not a true deep cycle.





Brock said:


> I take issue with this statement  since I have 24kw of sealed AGM batteries, 12v at almost 2000 amps.



(It's okay, I know how it happened)


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## Diesel_Bomber (Jun 21, 2006)

Brock- Those were my words. Yep, I should have added a caveat about AGM or gel cell deep cycles. 


Cheers. :buddies:


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## TedTheLed (Jun 21, 2006)

quoted on solar panels are for the very best available; including the Shell/Siemens -- they are not "low cost" panels. In fact contrary to expectations, the prices on solar panels have gone up over the years due to increased world-wide demand, (much German and Japanese use.)

the numbers I stated are completely accurate, and can be achieved within the costs I outlined. buying an entire "RV solar package" is a horse of a completely different color, usually including controller, inverter, converter, mounting frames, cables, etc. greatly increasing the initial $ outlay..

To reiterate; for $300 and some wire, you can run a couple ten watt lights, and get the energy expended back into the battery if tomorrow is a sunny day..

check the panel prices: http://shop.altenergystore.com/

http://www.infinigi.com/ (has a price matching and or beating policy)

edit: I just clicked on the above llinks and sure enough, prices have gone up a good 10% or so since I last checked..and the Shells are getting scarcer.."sign o the times" as Aretha would say..


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## tvodrd (Jun 21, 2006)

Last week I bought a couple Group 27, "Marine deep-cycles" from an Interstate battery dealer. (Model #SRM-27) They advertise 600 CCA/750 MCA and a reserve capacity of 160, and they are for my tank light proj. Rather than use my bench supply, I plan to buy a Sears charger. I will plead a little clueless as to "deep cycles," but as I understand it, you can discharge them farther and still recover capacity. Interstate doesnt provide a "75A" reserve capacity-rating for this battery like they do for their other deep-cycles. My load will be ~55A and I haven't a clue as to when the seriesed pair will drop below the 22V min that the searchlight will stay lit. 

Larry


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## Brock (Jun 21, 2006)

Wooops, sorry Brighteyes, weird…

Diesel Bomber, no worries, for the average battery user your statement was quite true that if it is sealed it is very likely to not be a true deep cycle, but if you know what AGM’s are you already know to much  I was trying to inject humor to those who knew what AGM’s were, aparently I am not so good at humor 

Tvodrd a very simplistic way to look at it is a battery can push out a lot of amps in a short time, like a typical starting battery or not as many amps for a longer time. In a starting battery you will tend to have lots of thinner plates closely spaced to give you the most surface area, thus allowing the most power transfer for the short term. In a deep cycle battery the plates will be thicker which will allow them to have a longer life when cycled and not warp under larger loads. So for your application where you want lots of amps for a short time a starter battery will give you that for less weight and a lot less cost, but likely won’t have the life span of a larger true deep cycle.

The number one cause of lead acid battery death is undercharging or not charging once used, the next leading cause is to use a cheap charger and literally boil all the acid out of the battery and forever damage the plates. A good charger will really help a battery live its full life.


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## Sub_Umbra (Jun 22, 2006)

Lotsa good stuff here.


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## Pydpiper (Jun 22, 2006)

So.. For this weekends power needs I will have both of my batteries, the "27" and the smaller "24" from my boat, again with the intentions of keeping power..
Would it be best to use up one then the other (at the risks pointed out throughout this thread) or to connect them both at the same time, if the later, how so?

This thread is great.. So much to learn.. 

Here is my new one, the "27", it was the largest capacity they carried.


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## Pydpiper (Jun 22, 2006)

Brighteyez said:


> Every travel trailer (at least in the last 25 years or so) has a 12V line to the pigtail. If you added the battery on your own, I suppose you could have neglected to connect that line to the battery. But I'm sure it's there and all you would need to do is connect it to the battery terminal (it might be connected to the 'battery' terminal of the trailer's power converter as well, just connect it to the battery and run another line from the battery to the converter.)


I wired this whole thing myself, trailer and truck side. If I am reading this correctly you are saying that the heavy 12V line I left out in my installation will charge my battery when the tow vehicle is running? I was always under the impression a deep cycle batteries required a slow, low current charge..
It would be easier and quieter to run the tow vehicle every now and then to keep the battery topped up..


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## Pydpiper (Jun 22, 2006)

One more question..
How long should the battery be on the charger to bring it from 12V up to 12.75? I know it is a vague question but I am only looking for a vague answer, an hour.... 8 hours?


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## Diesel_Bomber (Jun 22, 2006)

Pydpiper said:


> Would it be best to use up one then the other (at the risks pointed out throughout this thread) or to connect them both at the same time, if the later, how so?




The classic "don't mix different chemistry, age, charge level, or brand of batteries together" warning goes here. If you connect them together in parallel(you haven't mentioned needing 24v), the battery with the higher voltage will try and charge the battery with the lower voltage. While this won't lead to catastrophic failure, it won't do good things to battery life either. When charging, it'll be worse. If you charge to the full level for the lower voltage battery, then the higher voltage battery won't be charged. Likewise, charge to full for the higher voltage battery and you'll overcharge the lower voltage one. Separate would be my choice.

Have fun on your trip! :buddies:


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## TedTheLed (Jun 22, 2006)

to charge a battery from 12 v. to 12.75 ?

ok, first off remember that these relative voltage vs. capacity numbers are based on a temp. of 77F. there's a .084 volt drop for every 5 degrees of temperature drop..some places get cold at night so morning volt readings can appear low.. at 12 volts consider the battery 30% full. each added one tenth volt = 10% more capacity, so 12.7 = 100% (at 77 degrees F.)

since you want to replace 70% of the capacity of your battery you can estimate the number of amp hours it needs and supply them accordingly.

I forget what size you said the bank you'd be using was, but if it's say a 200 amp hour battery that means you need to put about 140+ 12 volt amphours back into it. With a 10 amp 12 volt charger this would take 14 hours..
..take the battery caps off to check the electrolyte level while you're charging..you will probably see the batteries 'fizzing' like soda, or an ocassional bubble, but they shouldn't be "boiling" (this would indicate too high a rate of charge) you don't want to 'top off' the liquid _before_ you start a large charge, because charging causes the liquid to expand and may run out the battery..top them off after the charging is complete..

it's better to charge your battery before it gets to 12 volts.. 12.3v or better
12.4v is as low as they should go if you want maximum life out of them.


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## Brighteyez (Jun 22, 2006)

Right. The car end connector should have a 12V line connection. All of the connections for RV connectors are color coded (sorry, I can't remember which color is for which, I think it's red or black for the primary 12V and yellow for an auxilary 12V), the colors are usually also stamped on the connector. You would usually use a heavy wire (10 gauge or heavier) with a 30A fused (or automatic resetting circuit breaker) line to the connector from the alternator. On the trailer end, the pigtail connector is also color coded, and that 12V wire would run to your battery (may also go to provide power for running/stop lights, electric trailer brakes, trailer brake breakaway switch, and refrigerator.)

While it will provide some level of charge for your battery, the level of charge is going to be dependent upon how long you drive and how much current is coming from your alternator, so I wouldn't expect it to fully charge a battery that is mostly discharged unless you plan on driving fairly long distances. To just run the tow vehicle to charge the trailer battery would be a very expensive proposition, even if you're in a province where gas is cheap (e.g. Alberta); it's not an efficient way to charge the battery. Generally it's more efficient to use a charger connected to a generator, or (depending on the generator) to use the 12V charge circuit from the generator. Insofar as noise, I'm afraid that too is dependent on the generator. Some of the current generators are so quiet that you have to walk up to them every so often to make sure they're running if there are a lot of people around. Of course, when you use the generator, do be aware that you're paying for the power (via gasoline) whether you're using all of it or not, so if you're going to charge the battery using the generator, it's also a good idea to switch the trailer converter over to AC and use the rest of the power for the trailer's power needs. 

While in theory, it may be better to run a long slow charge to bring a battery back to a full charge, it's not always feasible, and certainly not if you're using up the power faster than the charger can charge it. Though it theory, with a lead acid battery, it's best to keep it at full capacity all of the time. I'm afraid it's all a bit of a trade-off for convenience.



Pydpiper said:


> I wired this whole thing myself, trailer and truck side. If I am reading this correctly you are saying that the heavy 12V line I left out in my installation will charge my battery when the tow vehicle is running? I was always under the impression a deep cycle batteries required a slow, low current charge..
> It would be easier and quieter to run the tow vehicle every now and then to keep the battery topped up..


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