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Old 09-04-2018, 18:32   #1
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What battery do i have

Is a mexican one, the specs
It can deliver 295 minutes at 25 amps and will have at least 10.5 volts after that at 26.7 celcius.
Also it will deliver 1250 cranking amps at 0 celsius or 32 f.
That are the factory specs
So how many amps is my battery?
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Old 09-04-2018, 19:57   #2
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Re: What battery do i have

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Originally Posted by captprogreso View Post
Is a mexican one, the specs
It can deliver 295 minutes at 25 amps and will have at least 10.5 volts after that at 26.7 celcius.
Also it will deliver 1250 cranking amps at 0 celsius or 32 f.
That are the factory specs
So how many amps is my battery?
I think your question is really "how many amp hours is my battery"?
Given your data, it is about 123 AH.

However if you want to know the maximum amps the battery can deliver during starting, the answer is 1250 amps (at 0 C). It will of course deliver more at higher temperatures.

This all assumes the battery is new ; numbers go south after some use.
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Old 09-04-2018, 22:27   #3
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Re: What battery do i have

The AH capacity is less relevant for batts designed just for starting.
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Old 10-04-2018, 05:20   #4
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Re: What battery do i have

Greetings and welcome aboard the CF, progreso.
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Old 10-04-2018, 12:37   #5
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Re: What battery do i have

If your battery is specified with "Cranking Amps", you can be sure that it is a starting battery, not a deep cycle battery and is not really suitable for house loads on a boat.

"how many amps" is a bit meaningless. Drop a spanner across the termimals and it will give you thousands of amps.

If you mean "how much energy it can store", that is measures in "amp hours". You should probably read:
Amps v Amp hours v Amps/Hr

295 minutes @ 25 Amps is 123 amp hours. If you don't want to kill your battery in a hurry, you should probably figure on not drawing more that 50 amp hours from it before fully recharging it.
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Old 10-04-2018, 13:08   #6
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Re: What battery do i have

Reserve Capacity, or more accurately Reserve Minutes, is how long the battery can support a 25 amp load (on some batteries it is 75A) before dropping to 10.5 volts / 0% SOC.

RC or RM and Ah capacity are not one in the same and there is no direct computation that translates accurately between all lead acid batteries because the Peukerts constant varies..

Very often batteries that do not have an amp hour rating are also not usually a purpose designed deep cycle battery. Some still are, but have not been Ah tested or the vendor relabeling the battery just chooses not to publish the 20 hour Ah capacity.

A safe bet is to always buy a battery with a 20 hour Ah capacity rating, unless all you need is a starting battery. This ensures the battery has been tested and rated for such. You still can use the RC/Reserve Capacity number but this number should generally be divided by two to arrive at a close Ah capacity. There is not really an accurate conversion factor I I know of that works accurately across all batteries..

For example the Trojan AGM 4D battery is rated at 325 RC and 165 Ah. If you divide by 2 you would get 162.5 Ah's. This is usually a close approximation to the Ah capacity of a given battery but still not exact.

I have seen a fair number of fairly knowledgeable owners incorrectly assume their battery had XXX Ah's. The reality is that this battery was never rated in Ah capacity and only in RC/RM so this bank was nearly HALF the size it was thought to be which could prove to be an expensive miscalculation...

If you take your 295 minutes, and divide by two, you have what appears to be a 147.5Ah +/- battery but without knowing a Peukert for this battery it could be less. If the battery is even close to 147.5 Ah's then your discharge rate, for it to run 20 hours, would be about 7.38A.

You can look at Peukert this way:

A 25A load kills the battery in approx 4.92 Hours & yields 123Ah

A 7.4A load kills the battery in approx 20 hours & yields 147.5Ah to 163.5 Ah

The higher the discharge rate the less Ah capacity you get.

There are a few theories out there on how to approximate Ah capacity from RC/RM but none that I have found to be reliably accurate. Some books suggest to divide RC by 2 then to add 16 to that number, while others just say to divide by 2. There are a few others out there too. None have come up exact when applied to multiple examples of known battery 20 hour Ah ratings over-laid onto the RC/RM data..

This is because each battery has is own Peukerts constant. A battery with a Peukert of 1.11 won't translate the same as a battery with a Peukert of 1.49...

If you buy a specific group size battery eg: group 24, 27, 29/31, 4D, 8D etc., and the one you're buying has a significantly higher "rating" than others of the same physical size, that should be a red flag. A red flag that you are looking at an RC/RM rating rather than an Ah capacity rating.
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Old 10-04-2018, 16:12   #7
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Re: What battery do i have

^^ To add to Maine Sail's excellent explanation, it should be noted that the 20 hour rated Ah is not universal; Ah rating in Australia (and I believe the UK) is usually given at the 10 hour rate.
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Old 10-04-2018, 16:37   #8
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Re: What battery do i have

Interesting, 10 hours to "flat" 10.5V is a very fast rate.

Whichever rate you use just know that in markets like the US with zero regulations over these ratings,

most vendors can't be trusted, so you can only use the numbers to compare different lines within one manufacture's offerings.

Never between manufacturers.

The list of high quality vendors that are more trustworthy is pretty short.
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Old 10-04-2018, 16:50   #9
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Re: What battery do i have

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Originally Posted by john61ct View Post
Interesting, 10 hours to "flat" 10.5V is a very fast rate.

Whichever rate you use just know that in markets like the US with zero regulations over these ratings,

most vendors can't be trusted, so you can only use the numbers to compare different lines within one manufacture's offerings.

Never between manufacturers.

The list of high quality vendors that are more trustworthy is pretty short.
Your last sentence is pretty accurate!!!

As for the 10 or 20 hour rate, I guess it all perspective; I always thought that 20 hours was slow and that US manufacturers used 20 to make their product look better .

However the 20 hour does approximate real life use better I guess.

The takeaway is that you need to know the detail when looking at battery numbers and as you suggest, some of the numbers are rubbery.
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Old 10-04-2018, 18:08   #10
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Re: What battery do i have

Does the Blue top Optima that are easy to get in mexico are a deep cycle batteries.?
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Old 10-04-2018, 18:48   #11
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Re: What battery do i have

No. Great cranking, but don't last long cycling deep.

Look for 6V flooded GCs, ask your local golf courses what they recommend.

Solar outfits, or industrial, scrubbers etc.
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Old 10-04-2018, 20:18   #12
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Re: What battery do i have

the blue top is a deep cycle rated. the red top is a starting battery
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Old 11-04-2018, 07:04   #13
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Re: What battery do i have

False claims by the maker JCI, as with 99.99% 12V batts labelled as such and sold in mass market retail and automotive channels.

When they were manufactured by Odyssey / Enersys, inventors of TPPL AGM and the spiral wound tech, the "true deep cycle + dual use" claim used to be true.

Now you'd be very lucky to get 400-600 cycles drawing an average 50% DoD.

About on par with Deka AGM. See also DieHard.

Not true deep cycling in my book, 800 is IMO a bare minimum.

Odyssey's PC-2150 would be a fine choice if you want 12V sealed, but FLA 6V GCs would be much better value.
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