# Batteries



## Thor (Apr 7, 2004)

Ok everyone, I need some help.

I wish to upgrade my batteries but not spend a fortune. 1st I need a lesson on battery talk.

I need to know what to compare. I have been looking and have seen that batteries come with different spec's.

Volts - I know
CA - cranking amps (bigger the better) but how important
CCA - cold cranking amps (I assume the same as above except at a lower temp
Reserve Time - this is in minutes (current factory battery is 64min)
Amp Hrs.
20 hour rate - ???

I know the feedback is going to be 6v in series but they are expensive ($300 a pcs) Now I found a 6v battery at a farm store for $100 CA = 1000 the same 12v was CA 550 for $100.

I will be buying 2 new batteries so lets say I buy the 6v and put them in series.
This will give me 12v with CA = 1000. If I buy the 12v I will have 12v CA = 1100 which seems better????







Or do I stick with the reserve time - Try to max reserve time. I found a 12v with 206 min for $110 but did not have CA on it. They did not have a 6v. Will a pair of these batteries give me 412min of reserve?

Help. What are the important specs to look for when upgrading. I do not wish to spend an arm and a leg for batteries.

Thor


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## BlueWedge (Sep 11, 2005)

I don't know much about the differences but this will give you a good background 12 volt side of life


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## cookie9933 (Feb 26, 2005)

Thor,

Here is a link with a ton of good information about batteries:

http://www.windsun.com/Batteries/Battery_FAQ.htm

Bill


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## Y-Guy (Jan 30, 2004)

Thor the post on the 12volt side of life is one of the best. If you can take the time to read what he's written you'll be a battery expert in no time. Its well documented with tons of good info, I've used it and referred to it for years. Mark it though, you'll refer to it often.


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## Thor (Apr 7, 2004)

Thanks the info was awesome.

Here is a summary of what I found.

any typical RV storage battery you get will be a series arrangement of cells. Each lead acid cell will contribute a bit over two volts so a nominal 12 volt battery will have six cells. Note that the energy you get from a battery, its capacity, depends upon the total energy of all its cells whether connected in series or parallel. The connection arrangement just balances the current and voltage components of this energy.

While a battery is a series arrangement of cells, a bank of batteries may be arranged with both series and parallel configurations. When this is done, careful attention needs to be paid to balancing the currents through each part of the battery bank and protecting against internal currents caused by failure.

Series arrangement means that voltage in each cell is added by connecting the negative side of one cell to the positive of the next.

A parallel arrangement connects all the positive sides of each cell together and all the negative sides of each cell together. This means the voltage is that of the lowest voltage cell but the current capability is that of all of the cells added together.

Why series?
Series arrangements means fewer cells which means each can contain more stuff for greater capacity or can be built more rugged in a given amount of space. A series arrangement also means that a weak cell does not sap the energy of the others and any current going through the battery will just pass through a weak cell. This fact, that any load or charge current goes through all cells equally, tends to keep all of the cells at an equal state. It also means that a failed cell does not cause internal circulating currents. The failed cell may add some resistance and, since it does not contribute any voltage, it will show as a reduced battery voltage.

Why parallel?
A parallel arrangement means that current is shared between batteries and this means that each battery is exercised less vigorously which may increase usable capacity. Since removing any single battery will not change the voltage, there is a redundancy in batteries that can be useful in the event of failure (if that failure is detected early enough). Parallel is also useful in low voltage systems because it may be easier to find batteries at needed supply voltages. A failed cell in a parallel bank will sap energy as the other cells try to charge it. This can cause heat and loss of water in the failed cell as well as lost current capacity.

Capacity and current drain
The usable current from a battery depends very much on how fast energy is taken from the battery. Slower energy draws usually mean more usable capacity from the battery. Energy draw is usually indicated by current because a battery's voltage is relatively fixed by the battery design. Energy draw is called power and is the product of voltage and current. Energy capacity is a product of power and time.

The capacity gained by reducing energy draw or current drain in a parallel configuration versus a series configuration can be determined by evaluating Peukert's Formula T = C / In where T is how long you can drain current I from a battery that has a capacity C and an internal resistance characteristic n. For the case of two six volt batteries in series versus two 12 volt batteries in parallel, the comparison is when the current changes by a factor of two (when voltage doubles, current halves and vice versa for the same amount of power). The formula would be

Tp - Ts = (C / In) - (C / (2I)n) = C(2n - 1) / (2n In) = Tp ( (2n - 1) / 2n )

{subscript p for parallel and s for serial, serial has twice the current of parallel, the LCD (2I)n which is where the 2n comes from in the Tp term to be able to subtract the fractions, percent change divides both sides by Tp and then multiplies by 100 - check the algebra yourself and let me know if you think you see an error!}

So percent change from the low current to high current times is (2n - 1) 2n . When this is calculated, the range for typical batteries means drain times will be from 71% (worst case worth purchasing where n=1.25) to 65% (best case, n=1.05) changed from parallel to serial. In other words, doubling current will reduce time of draw from 65% to 75%. For the 40 amp hours available (discharge to 80%) at a 5 amp load, the parallel configuration could provide 8 hours of usable battery while the serial configuration would provide maybe 6 hours. This would be balanced by the batteries in series probably have a bit more capacity to start with.

Factors to consider
Longevity or Load? - when you go looking for a battery, you need to consider the balance between maximum load and longevity. This is the deep cycle versus starting consideration. Your potential maximum load will definitely influence how you wire your battery bank and may be important in choosing a battery that is designed to provide the necessary current. Usually, a microwave through an inverter is about peak load in most RV uses and this means maybe 150 amps out of the battery for a few minutes. This is not a problem for most batteries but does mean you will need low gauge wires and good connections.

Size . The battery, including wires and connectors, will need to fit in the available compartment. Smaller batteries will fit easier but bigger batteries will contain more energy.

Weight . more capacity usually means more weight. But you need to consider the impact this weight will have on your rig depending upon where it is placed and you also need to consider your ability to maintain (lift, remove, shove around for access) the batteries.

Cost - The price of the battery is one of your primary clues about manufacturing trade-offs. For instance, Trojan sells three 6 volt batteries that are all the same size costing from $55 to $95 (see Uve's site). The higher prices get you more capacity, less internal resistance, and lower cycle ratings. The lesson in this case is that, for a given volume or physical size, higher price gets you more capacity but less life.

Availability . Many battery types are difficult to ship so you are limited by what you can find at outlets in your area or you need to add shipping charges to the cost.

Capacity . Be careful not to consider just an amp hour rating as a capacity measure. Capacity is always amps times volts times time, so multiply the amp hour rating times the battery voltage to get a comparable capacity number. Also be sure to use equivalent amp hour ratings. The twenty hour rating is usually a common specification.

Warranty . The warranty on the battery will often tell you something about what the manufacturer and the retailer think about the battery's longevity in typical service.

Charge cycle ratings . This indicates how many times you can expect a battery to be discharged to a certain point and then recharged before it starts to fail. It is a ruggedness rating more than a quality rating. Watch out to make sure you compare cycle ratings for equivalent discharge levels. 80% and 50% are perhaps most commonly used.

Battery Type . The primary classifications of concern are whether or not the battery is a sealed type that can be placed inside or whether it needs a specially vented cabinet. This gets into access for maintenance and other factors as well. The type of battery will also be a factor in charging and in usage considerations.

Complications
The batteries and how they are configured are only a part of the entire system in your RV low voltage system. A typical RV system does not push any particular extremes so the design does not need to give undue weight to any single factor. This complicates the choice because you have many different considerations to play against each other and none of them will likely have any significant impact on the total result for typical RV usage.

Cell failures are fairly uncommon with even modest care to use and charging so that difference between parallel and serial configurations is not significant in this regard. Plan on replacing your entire battery bank every five to ten years.

Current drains average fairly low and you should only use 20% to 50% of the battery capacity so the change in current between the two configurations for a capacity reason is also insignificant in most cases. If every last drop is important, you will likely already have solar cells or a generator.

Since all you are looking for is twelve volts, anything past two batteries in the bank will require some sort of parallel configuration. As you add batteries to the bank, your attention will need to be on battery matching and cabling concerns.

You are more likely to make a difference by attention to maintenance, good wiring and connections to reduce resistance losses, careful choice of loads for efficiency, a multi-stage intelligent battery charger, and a few lifestyle habits that can drastically impact energy use.

Make your choice
For the simple case of adding a bit of capacity to an existing RV system, the question of parallel or serial is more of convenience than anything else. The current loads are typically low and the demands do not usually stress the battery charge sufficient to make the current versus capacity consideration very important. Parallel might provide a bit more capacity and serial might be a bit more reliable but the benefits can be easily outweighed by smart battery choices.

Long term boondocking puts a premium on capacity, but those in this group also usually have means to keep their batteries at a reasonable charge point so, again, the differences between serial and parallel are minor.

Inverter driven heavy use is another matter. Here, the battery loads still average fairly low but there are high peak draws as when you warm a cup of coffee in the microwave. In this case, it is the wiring and connections that will be the major concern and not the battery bank configuration. [unless you go for a 24v or 48v inverter]

These considerations indicate that, unless you have some specific requirement to match, battery bank configuration choice is mostly one of convenience. The factors of cost, size, type, and availability will likely dominate the decision tree.

Thor


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## LateralG (Feb 11, 2006)

Thor,

Outstanding summary ... thanks.


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## cookie9933 (Feb 26, 2005)

Thor said:


> Thanks the info was awesome.....The factors of cost, size, type, and availability will likely dominate the decision tree.
> [snapback]82348[/snapback]​


Yes, but did you make a decision about a battery purchase, or are you more confused than before?
















Bill


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## nynethead (Sep 23, 2005)

Thor,

Great summation, now my head hurts. I used two 12v marine batteries interconnected one side positive and the chassis ground on the second. This way all voltage passes through both batteries. Seems to work good, but have never dry camped so I do not know how long it would last.


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## LateralG (Feb 11, 2006)

My conclusions from Thor's excellent summary:

1) The right battery for me is the most (ampere-hours x volts) per $, and is readily available. 6 volt or 12 volt not important enough to overcome price and availability advantages.

2) Duty cycle in our application is VERY different from other applications. Our power drain is much less demanding than cranking a diesel engine on a zero-degree day, or powering a golf cart.

3) I see on the Sears web site that they have cold weather and hot weather batteries. I conclude that the hot weather batteries are better for us since they have thicker plates. Other than that, hot vs cold probably isn't a factor for us because of our duty cycle. If I still lived in Michigan, I would go for the hot weather battery.

4) I plan to watch the sales at Sears, TSC, and ??, then buy two of the best (amp-hours x volts)/$$ that will fit the 21RS I have ordered.

** I encourage firther discussion about my conclusions. Well-founded disagreements would be of particular value.

Questions:
I) What are the dimensions of the battery tray for the 21RS?
II) Does the trailer come from the factory with battery hold-downs?
III) Do y'all use a serious knife switch, or equivalent, to quickly disconnect battery power? If so, what switch, and its source?


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## CamperAndy (Aug 26, 2004)

LateralG - Please remember that you want batteries that are classed as Deep Cycle. These are better able to handle the deeper drains before recharging. Regular car batteries will be toast VERY quickly so it would be a false economy to buy starting battery.

I) - group 24 battery is a standard fit but should also hold a group 27 battery.
II) - not from the factory but the dealer should include them. My dealer included 2 batteries with boxes and hold downs. Some have reported getting just one battery with no box.
III) - They are recommended but not required. I prefer the keyed rotary switch to a knife switch.


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## WIOutbacker (Feb 12, 2006)

BlueWedge said:


> I don't know much about the differences but this will give you a good background 12 volt side of life
> [snapback]82341[/snapback]​


That's an awesome article. Thanks for sharing!


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## Steelhead (Nov 14, 2005)

LateralG, Iagree with Andy re. the deep cycle batteries. Be sure to get real Deep cycle and not just an auto battery or one that says Marine on it only and doesn't also say Deep Cycle.

As far as battery holder fit in your new OB, you will be wise to wait untill you can measure the battery support frames. Mine, albeit an older model, will only accomadate a group 24 size battery. I want to ungrade to two group 27's and probably dual 6 volts. therefore I am going to modify the frame to accomadate the larger battery size. You MAY need to modify too, if you buy larger than group 24 size. Don't know ,but would encourage you to measure first.

I too use a rotary key switch instead on knife switch.

I also believe that Amp Hour ratings are the best single measure of a batteries staying power while you are camping.

Dallas


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## LateralG (Feb 11, 2006)

Steelhead said:


> LateralG, Iagree with Andy re. the deep cycle batteries. Be sure to get real Deep cycle and not just an auto battery or one that says Marine on it only and doesn't also say Deep Cycle.
> 
> As far as battery holder fit in your new OB, you will be wise to wait untill you can measure the battery support frames. Mine, albeit an older model, will only accomadate a group 24 size battery. I want to ungrade to two group 27's and probably dual 6 volts. therefore I am going to modify the frame to accomadate the larger battery size. You MAY need to modify too, if you buy larger than group 24 size. Don't know ,but would encourage you to measure first.
> 
> ...


Rotary key switch: Make & source = ?
Deep Cycle: Make & source = ?


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## CamperAndy (Aug 26, 2004)

See this thread for the rotary switch of choice.

Perko switch


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## fishingmarlin (Nov 27, 2005)

Sounds like everyone is making this out to be more complicated than it is. Surely you have a walmart or sams club near you. They have 6V Golf Cart Batteries at $100 a pop. You can get into all the cranking amps and all that junk but a regular 6v run in series is all you need.

I don't know where you are seeing 6v for $300 but that is outrageous. I use 6v in the trailer and used to have them on the boat. The $100 ones worked just fine for me!!


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## CamperAndy (Aug 26, 2004)

fishingmarlin said:


> I don't know where you are seeing 6v for $300 but that is outrageous.
> 
> [snapback]82448[/snapback]​


Canadian dollars!!!!


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## Steelhead (Nov 14, 2005)

Trojan Batteries are really good. Can get the 12 volt deep cycle at Sportsmans Warehouse and Battery warehouse, who also has the 6 volt Trojans. 
However, you can get 12 volt deep cycle batteries at most places that sell batteries
including Costco etc. Some of those places will also have the 6v deep cycle, or golf cart batteries.


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## s'more (Jun 8, 2005)

I admit I'm no expert, but what I've heard from various sources, is that a strong choice is the Interstate U2200 golf cart battery ( 6 volt ). I saw it at Camping World on wednesday for $89.99, and you might be able to do better on the price if you shop around. action


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## old_tidefan (Nov 23, 2005)

Thor,
Thanks for the detailed summary!


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## Thor (Apr 7, 2004)

Prices I quoted are in Canadian $$ and a quick search on the internet. The $300 are the yellow top Optimum batteries.

Now if you get a gel battery the $$ go up again.

After all the input and reading here is how I am going to decide. (Deep Cycle)

Visit several battery stores:

Canadain Tire
Costco
Sears
Local Marina
RV Dealer
Walmart
Battery Warehouse (Sell factory 2nds)

CAA - I do not do alot of dry camping in the cold, so this is not important to me.

I am going to make a list of Volts, CA, Reserve time, Cost. I will be looking at batteries around $100 because that is my budget. What ever comes out ahead...that is what I am going to buy. If there is a close 1st & 2nd ..warranty will be the deciding factor.

Any other tips for my list?

Thor


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## LateralG (Feb 11, 2006)

How do we know that a battery that claims "deep cycle" really is?

Is it enforced, and more descriptive than "high performance", "Heavy duty", etc.?


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## CamperAndy (Aug 26, 2004)

"Enforced"?? Not likely but it does refer to a design feature of the battery. The plates are a different thickness and for the life of me at this moment I can not remember if they are thicker or thiner. So I will search for the answer to my question but in answer to your question they are different.

On edit:

Okay the answer to my question is that the plates are thicker and are solid in the best true deep cycle batteries.


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## shake1969 (Sep 21, 2004)

Thor said:


> Tp - Ts = (C / In) - (C / (2I)n) = C(2n - 1) / (2n In) = Tp ( (2n - 1) / 2n )
> 
> [snapback]82348[/snapback]​


Crap, no wonder I'd pop a breaker every time I plugged in the coffee pot.

I was using a 3 instead of a 2!


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## LateralG (Feb 11, 2006)

CamperAndy said:


> "Enforced"?? Not likely but it does refer to a design feature of the battery. The plates are a different thickness and for the life of me at this moment I can not remember if they are thicker or thiner. So I will search for the answer to my question but in answer to your question they are different.
> 
> On edit:
> 
> ...


I'm still a bit uneasy on this. What prevents a manufacturer from labeling a standard battery as "Deep Cycle".

Are there manufacturers that we trust enough to give them more of our money because they say theirs is deep cycle?

Is there more to deep cycle than thicker plates? The Sears hot weather battery has "thicker" plates.

Please understand that this is not an attack or a challenge. I'm just terminally curious, and have been deceived by misleading manufacturers' claims.


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## cookie9933 (Feb 26, 2005)

I would say that there are differences in construction between "regular' and deep-cycle batteries. And that the construction differences result in performance differences. Your point is well taken because someone conceivably could label their standard battery as deep-cycle and deep-cycle your wallet.









As in anything else where you cannot independently verify the makeup of a product, buy a brand with a good reputation. You will probably get what you pay for.

Bill


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## Thor (Apr 7, 2004)

shake1969 said:


> Thor said:
> 
> 
> > Tp - Ts = (C / In) - (C / (2I)n) = C(2n - 1) / (2n In) = Tp ( (2n - 1) / 2n )
> ...


LMAO.

Deep cycles have ticker walls that allows them to discharge without damaging the battery. Is heavy duty and deep cycle the same thing?

Thor


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## California Jim (Dec 11, 2003)

LateralG said:


> I'm still a bit uneasy on this. What prevents a manufacturer from labeling a standard battery as "Deep Cycle".
> 
> Are there manufacturers that we trust enough to give them more of our money because they say theirs is deep cycle?
> 
> ...


Just check the batttery weight. Extra lead or a lack thereof will soon be apparent. Given the choice between batteries with the same specs, buy the heavier one.


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## LateralG (Feb 11, 2006)

California Jim said:


> LateralG said:
> 
> 
> > I'm still a bit uneasy on this.Â What prevents a manufacturer from labeling a standard battery as "Deep Cycle".Â
> ...


Now we're talking.


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