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Old 01-16-2011, 04:41 PM   #1
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New 6 Volt House Batteries,

Energizer Golf Cart batteries from Sams Club, EGC2 made by Johnson Controls. At only $150 OTD for 2 seemed like a good deal.
However, I'm not sure what I got and Sams didn't seem to know much about batteries either. I hope I got some thing at somewhat comparable to my original batteries.
Many people say the Trojan's have 220 Amp Hr.
I have no idea how many amp hrs these have. They say
105 Min Reserve Capacity. Is this 105 # a direct comparison to the 220 # compared on some other batteries? If so, maybe I didn't get such a great deal after all. My last batteries were original and the lasted 6 yrs. They were Workaholic (U 2200) was the only readable # on it.
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Old 01-16-2011, 05:11 PM   #2
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Rule of thumb is to times the RC by 2, so 105x2=210 Ah... well within the range.

edit:

Quote:
We just bought 4 of the Sam's Club GC-2 Interstate batteries in Yuma, that have 210AH capacity for $67/ea. For the difference in price, even if there do go bad in 4 or 5 years you can buy a second set and still be way ahead. However, we are finding them to hold a charge as long or longer than the 225AH batteries they replaced.
Discussion: http://www.motorhomemagazine.com/boa...d/23895703.cfm
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Old 01-17-2011, 12:30 AM   #3
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All wet cell lead acid batteries have an energy capacity of about 45 watt hours per kilogram (re batteryuniversity.com). That means you have about 10 to 15 usable watt hours per pound at the 50% SoC, which is usually considered the optimum cost efficiency nominal discharge target.

Don't get hung up on the many myths about batteries that abound in these discussions. Also don't get hung up on small differences as available battery capacity can vary by more than 10% from such things as temperature, use profile, age, and cycle to cycle variance.

If the batteries you got weigh about the same as the old ones, fill the same battery box, have a good warranty from a reputable retailer, and you use and maintain them properly, they should do as good or better than the previous batteries you had.
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Old 01-17-2011, 09:21 AM   #4
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According to this article, the RC rating is 2X the AH rating, so you need to DIVIDE by 2 rather than multiplying by 2. That would mean a 105 RC battery is only 52 AH.
Battery Confusion - Amp Hours vs. Reserve Capacity - SailNet Community

Trojan rates their T105 at 447 RC.

RC (Reserve Capacity) is the number of minutes at a 25 Amp discharge rate. AH is the number of amps that can be sustained x 20 hours, e.g. 10 amps x 20 hours = 200 AH.
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Old 01-17-2011, 09:45 AM   #5
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When using the reserve capacity as a measure of battery energy capacity, you have to keep in mind the Peukert phenomena.

The usual 20 hour rate for battery capacity means a draw of about 60 watts for a typically sized RV battery. For a 6v battery, the RC rate is 150 watts or more than twice that current drain. That means it is going to show quite a bit less energy available from the battery.

This is one of the issues behind why 'use profile' can be very important in considering the accuracy of battery measures.

(It can also get 'interesting' in the 6v vs 12v brouhaha as the 20 hour rate is not a voltage dependent measure while the RC is and that can be misleading)

These sorts of things are why I suggest using battery weight as the primary capacity measure. That is a valid and objective measure that tells you what you need to know without the 'nuances' or misplaced precision or other such stuff that pollutes battery discussions.
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Old 01-17-2011, 11:59 AM   #6
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Quote:
Originally Posted by Gary RVRoamer View Post
According to this article, the RC rating is 2X the AH rating, so you need to DIVIDE by 2 rather than multiplying by 2. That would mean a 105 RC battery is only 52 AH.
Battery Confusion - Amp Hours vs. Reserve Capacity - SailNet Community

Trojan rates their T105 at 447 RC.

RC (Reserve Capacity) is the number of minutes at a 25 Amp discharge rate. AH is the number of amps that can be sustained x 20 hours, e.g. 10 amps x 20 hours = 200 AH.
Hmm.. I might have that backwards... However, I really dont see that battery as having only a 52aH rating. In fact, I know it doesnt. The proplem comes from the way they are rated and at which amp draw. The site you linked to uses the RC numbers tested using a 25 amp constant draw. The one listed on the Costco battery is from the 75 amp constant draw test..

So, to be more precise, IF the RC is from the 75 amp test, use x2. If from the 25 amp test, /2.

Here's what I mean - taken from a Johnson email response:
Quote:
Abel,

Here is the information you have requested.

GC2 US Battery Red Top:
Amp-Hour at the 20 hour rate: 220 Ah
Minutes at 75 amps: 110 minutes
Minutes at 25 amps: 425 minutes

Thank you

Janine
Trailer Life Magazine Open Roads Forum: Tech Issues: Costco 2-GCS Batteries


And again:
Quote:
6Volt

GC2 Enertec product Blk/Blk: SAM'S CLUB/Costco
Amp-Hour at the 20 hour rate: 225Ah
Minutes at 75 amps: 110 minutes
Minutes at 25 amps: 447 minutes
Costco 6V GC Batteries (Johnson Control): Opinions?? - Page 2 - DIY Electric Car Forums

Again: costco 36V battery / vs / trojan / exide. ??? - Page 5

And, good reading on the 2 RC ratings: Two battery questions | Caravan Camping | Camping How

https://www.rv.net/forum/index.cfm/f...d/tid/23284931

Note: at the 75 amp, the Trojans only last 110-115 minutes : Trojan Battery Company
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Old 01-17-2011, 01:28 PM   #7
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Let's not confuse things, what say?

RC is defined as "the number of minutes a battery at 80 degrees F can be discharged at 25 amps and maintain a voltage of 10.5 volts for a 12 volt battery." There is a set of such carefully defined terms for battery specifications that need to be properly understood in order to be able to interpret the spec properly.

The reason why you'll see the 20 hour rate along with the RC along with other battery energy capacity measures (especially for batteries intended for RV or marine use) at various power draws is because of the Peukert phenomena. The faster you draw from the battery, the less available energy capacity it will have. It is an exponential function and there is a 'peukert coefficient' to describe it. For the batteries here, that coefficient is about 1.2 or so. It can be calculated from the 20 hour and the RC specifications.

The lesson to be learned is that you have to know your 'use profile' or how you draw energy from the battery in order to nail down a realistic battery capacity from the specs - and it is easy to have numbers that don't reflect reality very accurately. That is a major flaw in many of the resources and discussions I have seen.

There are also many other issues that get involved as well as you can see in the definition cited. Note how the end point is defined and the temperature spec, for instance.

All of the numbers and the links and whatnot can be interesting but they get so much into detail they often forget the big picture. Take care and don't get lost in the forest examining tree bark when what you need is a picture of the forest.
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Old 01-17-2011, 01:38 PM   #8
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Bryan this article from the University of Hawaii confirms what you say, and defines the RC to AH conversion more clearly: Amp/Hours = (Reserve Capacity / 2) plus 16
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Old 01-17-2011, 09:23 PM   #9
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There are TWO RC ratings: 25 AMP AND 75 AMP!! The 25 amp is the most common, but saying there is only one correct definition is incorrect.

How can you say to take the RC listed (105mins @75amp) and /2? There is no way that battery is a 50aH battery.. none.

However, if it says to take a 25 amp RC (some high number, like 440) and /2, then sure... But what about the batteries showing the 75 amp RC? Do you divide by 2 still?

If so, please explain why, because you are then telling a lot of people that their batteries are crap.

Its not me whos confused the matter, its the OEM's..
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Old 01-17-2011, 09:27 PM   #10
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Originally Posted by Ray,IN View Post
Bryan this article from the University of Hawaii confirms what you say, and defines the RC to AH conversion more clearly: Amp/Hours = (Reserve Capacity / 2) plus 16
Link doesnt work...

I assume you meant this page? http://www.chem.hawaii.edu/uham/bat.html That is using the RC25 (25 amp) method..
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Old 01-17-2011, 09:33 PM   #11
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O boy, battery topics get over my head in a hurry.
I'm thinking that these are typical 60 LB 6 volt batteries, probably 220 amp hrs.
Would that be 440 amp hrs since I have 2 of them?
My normal expectations would be to be able to run a 27" TV set thru a 1500 watt inverter for 2 or 3 hrs, have light in the MH for maybe 3 to 5 hrs and have enough reserve capacity to run the 31,000 BTU furnace for maybe 10 min per hr for up to 12 hrs, and be able to start the genny in the morning.
Is it reasonable to expect these $75 Sams Club batteries to be able to do this? Or should I run the generator until 10 PM or so?
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Old 01-17-2011, 09:37 PM   #12
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Quote:
RC is defined as "the number of minutes a battery at 80 degrees F can be discharged at 25 amps and maintain a voltage of 10.5 volts for a 12 volt battery."
And, your actually wrong about that definition.. Not your fault, though, it been said enough times people believe it...

Reserve Capacity - The number of minutes a battery can be discharged at the specified rate (25, 56 or 75 amps) at 80 degrees Fahrenheit and maintain a voltage above 1.75 v/cell.
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Old 01-17-2011, 09:47 PM   #13
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Originally Posted by max49 View Post
O boy, battery topics get over my head in a hurry.
I'm thinking that these are typical 60 LB 6 volt batteries, probably 220 amp hrs.
Would that be 440 amp hrs since I have 2 of them?
My normal expectations would be to be able to run a 27" TV set thru a 1500 watt inverter for 2 or 3 hrs, have light in the MH for maybe 3 to 5 hrs and have enough reserve capacity to run the 31,000 BTU furnace for maybe 10 min per hr for up to 12 hrs, and be able to start the genny in the morning.
Is it reasonable to expect these $75 Sams Club batteries to be able to do this? Or should I run the generator until 10 PM or so?
When you hooked batteries up in series, you add to the voltage, but not to the Amp Hours. So 2 220Ah @ 6 volts hooked in series would be 220Ah @ 12 volts. If you hooked them in parallel, then the voltage stays the same, and the Amp Hours would increase, ie; 2 180Ah @ 12v in parallel would be 360Ah @ 12v.
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Old 01-17-2011, 09:52 PM   #14
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I'm like Max as long as I can use my batteries say on a overnight boon dock and they can be recharged to the next stop I'm happy.
I replace my 6V wets with 12V AGM Blues from Sams club.
When we discuss the tech information it would be nice if two points of view could meet common ground for all of us.
Just my thoughts.
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