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Old 26-05-2012, 17:10   #1
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A Curious Battery Question

My generator start battery receives the standard alternator charging regimen as would a regular flooded battery when the generator is running.

When the propulsion engine, or the shore side battery charger, is operating the generator start battery is charged according to the AGM requirements of my house batteries.

Hence the question:

Given the two differing charging profiles, would a standard flooded battery last longer, or would an AGM battery be a better choice for the generator start battery?

Generally, time on the hook might last as long as two or three weeks before there would be an opportunity to connect to shore power or run the engine for an extensive (more than one hour) time.

Anyone have any empirical data, or at least a semi-thoughtful wild ass guess???
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Old 26-05-2012, 18:31   #2
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Re: A curious battery question

Can a Battery be curious??..... Looking at the charge rates for AGM and flooded, it seems safe enough to charge flooded batteries with a battery charger set on AGM. The flooded battery has a higher internal resistance then AGM so it will charge slower.

Though being a start battery it will not need a lot of charging anyway. Based on the lower float votage settings for AGM, your safe enough with the flooded start battery on the agm charger setting.
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Old 26-05-2012, 18:37   #3
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Wait now my dyslexia is setting in. Agm have a higher charge then flooded. You will boil off the start bat at those rates. My simple stupid solution was to have all Agn bats. Works fine for many years now.mire sophisticRd stuff is probably better.my Agn have higher charging values then flooded cell?
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Old 27-05-2012, 06:39   #4
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Re: A curious battery question

In my case AGM would last longer than lead acid because I am hopeless at remembering to service the water level in a lead acid battery.
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Old 27-05-2012, 06:47   #5
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Re: A curious battery question

Here's a solution. Optima batteries are great starting batteries, reasonably priced, available most everywhere and are AGM.
Optima Blue Top AGM Battery - Deep Cycle Marine Batteries by Optima
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Old 27-05-2012, 06:53   #6
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I have Optima batteries and have had them for 4 seasons now with no issues.
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Old 27-05-2012, 07:00   #7
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Re: A curious battery question

AGMs and flooded batteries have virtually identical charging profiles. Problem is, you'll find slight differences in different texts and manufacturer's "instructions". These last, believe it or not, are often developed by sales and marketing folks, not by the engineers or designers of the batteries.

IMHO, no problem charging an AGM with a flooded battery profile, or vice versa.

Keep in mind that in general all recommended voltages are too low for adequate charging and for floating. They're quite conservative.

RE: longevity, flooded batteries are likely to outlast AGMs if they are maintained properly. If not, the AGMs might outlast them.

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Old 27-05-2012, 09:44   #8
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Re: A Curious Battery Question

Optima are great batteries BUT they have two drawbacks. They are JCI's "premium" brand name and as such they are priced about 30% higher than conventional flat-plate AGM batteries, even though spiral-wound batteries are supposed to cost less to make. With AGM already being ~30% more than wet lead, Optimas are damned expensive. Then they also provide about 10% less capacity than any flat-plate battery in the same group size, because they are a "box full of tubes" instead of a box full of flat plates.

While AGMs have been made to match wet lead charging "more or less" for a decade now, they aren't all the same. The charging profiles usually overlap but if the wet lead profile you are using is on the high side, it could be too high for the AGMs and overheat them, causing some permanent loss of electrolyte and battery damage. The only way to tell, is to measure the outputs from both systems, and do so to a confirmed accuracy of 1/10th volt. Then see what is right for the actual batteries you have, because all brands are not the same either.

Probably OK? Sure. But "probably" often means a 3-4 year battery life. If that's OK with you, then probably is good enough.
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Old 27-05-2012, 10:10   #9
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Re: A Curious Battery Question

Never had a curious battery, had some obstinate ones though! Optimas are expensive for sure, depending on which level of quality you buy (blue, yellow, red?) At the boat shop we had 2 out of 50 bad from the get go.... may have just been an anomaly though....
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Old 27-05-2012, 13:24   #10
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Re: A Curious Battery Question

The Optima color codes are nothing to do with quality. Redtops are SLI batteries, with thinner plates for higher impulse power. Yellowtops are like many other batteries with yellowtops, dual-purpose designs. And their Bluetops are the true deep-cycle batteries with thicker plates.

The warranties also differ.

Odd that you got so many DOAs, since the spiral construction is supposed to make assembly simple, cheap, and reliable. And JCI usually build good products.
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Old 27-05-2012, 13:41   #11
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Re: A Curious Battery Question

Yeah, I thought it was odd too. Govt contract so those batt's were specified in our bid. Hopefully just a fluke....
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Old 29-05-2012, 05:58   #12
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Re: A Curious Battery Question

Quote:
Originally Posted by hellosailor View Post
The Optima color codes are nothing to do with quality. Redtops are SLI batteries, with thinner plates for higher impulse power. Yellowtops are like many other batteries with yellowtops, dual-purpose designs. And their Bluetops are the true deep-cycle batteries with thicker plates.

A bit of a correction here: Blue top Optimas are the "Marine" versions, with marine terminal types rather than just the round automotive terminals. The 34M blue top is exactly the same as the 34 red top, except for the terminals. It's a starting-oriented batt.

The other blue tops, model numbers starting with D, are "dual purpose", with slightly more deep cycle characteristics. They are not very cost effective deep cycle batts - comparing their deep cycle capacity to better AGM's for that purpose such as Deka and Sears Platinum.

I've had many Optimas (red and blue tops) and Deka AGMs. The Optimas were good starters.
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Old 29-05-2012, 06:10   #13
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Re: A Curious Battery Question

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Originally Posted by NewMoon View Post
. . . The Optimas were good starters.
I would agree that the Optimas are "job-specific" to starting an engine/genset and not well suited for other applications. There are better and more cost effective batteries for house bank, etc.

But as a engine start battery I have been very happy with mine for 6 years now.
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Old 31-05-2012, 10:37   #14
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Re: A Curious Battery Question

Put new batteries in my boat yesterday:

4 Deka GC 15 and 1 Deka 24M7, same set up as before.
Checked the maintenance log and realized the old Deka batteries had been in there for 6 years and 7 months...Pretty impressive, but the house bank had lost some oomph: The fridge compressor would shut down at night for low voltage, but as soon as the sun came up, the panels would up the voltage enough for the fridge to start again.
Lights, music and cooking etc would not affect the voltage at night, only the compressor.

Got a good price on the Deka batteries, highly recommended.

(No, I don't have stock in the company, just passing on good info to fellow cruisers)
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