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Old 05-16-2007, 06:56 AM   #21
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Rodney,

My '06 19 CCD came with 2-12VDC liquid cell Interstates in parallel. My choices were to directly replace them with a pair of GPL24-CT AGMs, or go with a pair of 6VDC golf cart AGMs in series. I chose the latter for their better draw-down characteristics and overall bomb-proof build qualities. The mod on the battery box was minimal.
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Old 05-16-2007, 08:42 AM   #22
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Hi Gen,

Here's a brief summary of what I've learned over the last few months from searching this forum and reading Harold Barre's book "Managing 12 Volts." Any of the experts here (Randy, Lew etc..) please feel free to correct me.


It all depends what you are looking for in terms of battery capacity. Lets say for example that you want to have 200 amp hours of battery capacity in your Airstream. There are a few ways that you can go about doing this, each with its own pros and cons.

1. SINGLE BATTERY

Have a single 12v 200 amp hour battery.

Cons: This battery would be very large, almost 2 feet long and quite heavy (probablly in the 140-160 pound range)


2. PARALLEL

Have two 12v, 100 amp hour batteries connected in parallel. When you connect batteries in parallel, the voltage reamins the same, but the capacity doubles. So your end result would be a 12v 200 amp hour battery bank.

Pros: If you ever have a bad battery, the remaining battery will still be able to supply 12 volts to your system, pump, lights but more importantly, your breakaway switch (which uses 12v) for emergency braking.

Cons:The two batteries that you parallel must be exactly matched. If they are not equal a small current can develop between them. The stronger battery will try to charge the weaker one until they are both equal, and you will be left with two partially discharged batteries.


3. SERIES

Have two 6v, 200 amp hour batteries connected in series. When you connect batteries in series, the voltage doubles, but the capacity remains the same, So your end result would be a 12v 200 amp hour battery bank.

Pros: As others have discussed, because of the rugged design and thicker plate construction, good quality 6v batteries can withstand deep discharging, be recharged fairly fast, and will still give excellent cycle life.

Cons: If you ever have a bad battery, since the remaining battery is only 6v you will not be able to power your 12v systems lights, pump, breakaway switch.


With respect to your question of cost, in examples 2 and 3 you are buying two batteries, and from my research a 12v 100ah battery is roughly the same coast as a 6v 200ah battery.

In terms of battery charging, the charger will "see" each of these three setups the same, as one 12v 200 amp hour battery.


Hopefully this helps.


Patrick
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Old 05-16-2007, 09:51 AM   #23
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Patrick:

Thank you for this very clear and worthwhile contribution.

If I do an “apples to apples” amp-hour comparison, it seems that Lifeline costs 3 times what an ordinary battery like an Interstate does.

Do the advantages outweigh the cost differential?


Sergei
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Old 05-16-2007, 11:06 AM   #24
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Hey Patrick,

Ya did good!

I had that diagram (in color) on another battery thread.

Sergei, for me and others, the durability, ease of re-charging, extra draw-down capacity, AND 5 year guarantee make the Lifelines THE choice. Not to mention that fact that you'll NEVER have to look at water levels again!

I have customers with 6 year old Lifelines in their MoHos and they're still going strong! I doubt ANY Interstate can come close!
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Old 05-16-2007, 11:07 AM   #25
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Quote:
Originally Posted by SmokelessJoe
Patrick:

Thank you for this very clear and worthwhile contribution.

If I do an “apples to apples” amp-hour comparison, it seems that Lifeline costs 3 times what an ordinary battery like an Interstate does.

Do the advantages outweigh the cost differential?


Sergei

Great question Sergi, I am struggling with that as well
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Old 05-16-2007, 02:26 PM   #26
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In the end it's not a one size fits all answer.

Liquid cell lead acid still has it's place. It's by far the cheapest initial investment. For a competing technology to even come close to amortizing the cost it will have to last 2-3 times as long. Will it? Depends on how you use and treat the battery. If you over charge a sealed "maintenance free" battery (regardless of type) it's probably toast. On a conventional liquid cell you can top it off with distilled water and, provided the overcharging wasn't too severe recover virtually all of the original potential. So if you still have an old Uni-volt or know that you aren't the most conscientious maintainer of battery condition lead acid may be for you. There's lots of other ways to kill batteries, too hot, too cold, discharging to far, not recharging immediately, etc. How you treat the battery will have more to do with how long it lasts than the type of battery you use.

The big advantage of a "maintenance free" battery is that you don't have to monitor the eletrolyte level and it's FAR less likely to leak or vent noxious fumes. As stated above this is a double edged sword. A battery almost always dies becase of the failure of a single cell (3 cells per 6V, 6 cells per 12V battery). With a flooded lead acid it's easy to detect an ailing cell with a hydrometer. With a sealed battery you'll see a drop in "fully charged" voltage but you can't tell if it's because all the cells are aging equally or if one cell is about ready to croak.


Another clear cut advantage of the Gel cell and AGM batteries (and some flooded "maintenance free") is a greater resistance to self discharge. Unless you full time or are meticulous in your maintenance this is likely the biggest factor in RV use. Not only do the Gel and AGM batteries discharge at a slower rate but they recover better than flooded cells. I think in this respect Gel cells, perhaps because it's a more mature technology have a slight edge over AGM. To a great extend this is going to depend on the technology used and will be reflected in the cost.


Comparing AGM and Gel cells most gel cells are going to be cheaper to buy and, if treated correctly provide a greater (~20) number of discharge/charge cycles. AGM has a higher current capacity. That's important in a golf cart but I don't see it as a factor in a trailer. A giant MoHo with inverters that run full size applicances; now that's a different kettle of fish. The AGM has a faster recharge time. OK, if you're recharging from the genset it's REALLY nice to be able to run it for a shorter period of time. Howver, both types of battery will last longer if charged slower. AGM batteries also suffer failure modes such as the formation of dentrites between cells and cell separation which make them slightly less robust (resistive to abuse) than gel cells. On the other hand AGM technology is a little better at handling temperature extremes.

You pays your money and yous takes your chances :+)

In order of cost:
Conventional Flooded cell lead acid
Sealed "Maintenance Free" flooded cells (Pb/Ca)
Gel cells
AGM

As far as 12V vs 6V it's purely a matter of packaging. All lead acid batteries are a series of 2V cells. What sizes, features, etc. the manufacturers offer in each is driven by market conditions. In the end you need 12 volts so always consider the cost and size of 2 6V batteries compared to a single 12V of equal type and capacity. Amp hour ratings are the only convenient way to compare capacity but don't directly compare amp hour ratings between different battery technology. This is another case where how you use/abuse the batteries has a major impact.

-Bernie
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Old 05-16-2007, 03:40 PM   #27
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All this about batteries has me thinking, especially since I need to replace the two lead/acid batteries that I have. Through my own negligence, I let them become dry this past winter because I left them connected with the shore power plugged in.

Question: What type of charger/converter do I have in my '04 ? Is it multi stage? Will it go into float mode when the batteries are fully charged?

Thanks.....
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Old 05-16-2007, 06:17 PM   #28
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Originally Posted by romap
All this about batteries has me thinking, especially since I need to replace the two lead/acid batteries that I have. Through my own negligence, I let them become dry this past winter because I left them connected with the shore power plugged in.

Question: What type of charger/converter do I have in my '04 ? Is it multi stage? Will it go into float mode when the batteries are fully charged?

Thanks.....
Ron,

I believe that Airstream uses Parallax single stage converters in all of their product. That's why I went to a WFCO 3-stage right out of the box. I had the OEM Interstates in there for 10 months before going to AGMs and never had to add water to them with the WFCO. Now of course, there ain't much to do except use the darn things and keep it plugged in.

One other great benefit of AGMs is the very low internal resistance, like 2-3% as opposed to wet cell's 30% or so. What that means is you can leave an AGM unplugged and assuming NO DRAW on the battery, they will only loose 3% of their charge avary month or so. If you put them away at full charge of 13.2 volts, they will still be at 12.4VDC after 60 days.

They also re-charge much quicker due to this feature in that high internal resistance does not have to be overcome by the charger to start the charge voltage flowing. The AGM accepts the charging voltages much more readily.
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Old 05-16-2007, 08:46 PM   #29
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Pat, you have it well said, and lots of great info in this thread from others too.
Lew, that was a great way to explain the starting voltage although that it regulated. I think the low resistance actually allows more initial amperage with the same voltage, don't ya think?
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Old 05-16-2007, 09:33 PM   #30
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Lew,
Thanks for your response. Do you think that it would be wise to go with AGM's with the stock charger? What damage could be done to AGM's by overcharging?

Thanks...
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Old 05-26-2007, 05:54 PM   #31
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Lew,
Thanks for your response. Do you think that it would be wise to go with AGM's with the stock charger? What damage could be done to AGM's by overcharging?

Thanks...
Ron,

A single stage charger in effect puts 14.2-14.4 volts to the battery all the time. The beauty of the 3 stage units is that after reaching a certain charge level....say 80%, the charger automatically drops the voltage for the 'acceptance' charge, and further reduces it at a higher state of charge for the 'float' charge. Some folks might call this last charging state the 'trickle' charge.

AGMs should be removed from the charger once they are fully charged to around 13.2 volts. Even though they have no free liquid electrolyte, the acid that is fully absorbed in the glass sponge WILL GAS thru the vent if the battery is overcharged and potentially damage the cell.

Hope this is clear. Just another reason to use a 3-stage charger......you don't have to worry about the battery state.......it's all automatic!
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Old 05-26-2007, 06:12 PM   #32
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Ron, I don't know how many batteries you have but if you are going to be buying multiple AGMs, ($200-300 each) the expense of a new converter (charger) isn't that much more. ($200 plus or minus).
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Old 06-03-2007, 04:06 AM   #33
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I think the low resistance actually allows more initial amperage with the same voltage, don't ya think?
Agree with you Randy on this statement. I believe lewster's meaning was internal leakage instead of internal resistance. Am I right lewster?
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Old 06-03-2007, 06:23 AM   #34
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Originally Posted by FrenchBern
I think the low resistance actually allows more initial amperage with the same voltage, don't ya think?
Agree with you Randy on this statement. I believe lewster's meaning was internal leakage instead of internal resistance. Am I right lewster?
FB,

You are right, but they are the same thing....just terminology. Ohm's law states that: voltage (E) = current (I) X resistance (R) so a battery with lower internal resistance will accept a greater current at any given voltage.

It is the internal resistance in a battery that causes it to self-discharge. The greater this resistance, the quicker the charge dissipates.
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