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Toddavid

Convince me: AGM vs lead acid

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Current batteries are 5 year old starting/deep cycle type, group 27, Deka. Couple of cells on one battery look to be marginal using my specific gravity gauge.

Same brand/spec lead acid are a third the cost of AGM.

Why shouldn’t I just buy lead acid replacements?

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Agm have their purpose but not any better for many applications.

If your engine manufacturer specifies AGM (like a Verado outboard) then follow the recommendation. Large fast draw like thrusters or electric steering - agm. Fast recharge cycles for tournament fishing -agm. Difficult location and limited access - agm. Regular IO boat with 2 batteries and reasonable access - flooded for sure.

For the boat in your signature, Deka 27m6 flooded batteries are more than sufficient as are the Interstate equivalents. You won’t see any benefit from AGM other than your wallet will be easier to carry with less money left in it.  

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Are the tops of any cells NOT covered by water? Where they EVER not covered ?     If always kept covered ?  You would have got more years of service at 1/3 of the cost.

In boats & cars driven by normal people.  Lead acid is excellent.

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All I can say, I have 5 of them, Two for starting and 3 for the house. Three of them are 10 years old and the other 2 are 8 years old and still going strong. I leave them in the boat in the winter for at least 6 months with out charging them until the spring.

When I reconnected the batteries and shore power 2 weeks ago. The charger was displaying a rate of 2.5 amps. It only took about 2 hours before the charger when into sleep mode.  Not bad for 5 batteries over 6 months sitting in the boat over the winter.  Also, when we go away, we sometimes take a mooring. The 3 batteries will last around 24 hours, running the fridge, lights, sump and water pump and the head.  

 

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I just replaced one in my wife’s Jeep.  7 years old and 120k miles on it.  OE battery.  Only reason I changed it is because I knew sooner or later it needed to be done.  Probably dumb I did it.

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My dealer installed Interstate Marine batteries on my 256 SSX in 2008. 10 years later, one tested good, and the other tested great, but I caught a sale and replaced in kind as I figured I was running on borrowed time.  ECM's don't like deep cycle batteries so Merc specifies two starting batteries, and I went with the same Interstate 1000 CCA Marine for around 103 each. Never found a reason to spend the extra money on glass mat batteries as my house loads are minimal. Engines like the high surface voltages provided by a starting battery as it provides excess starter current while not robbing initialization current away from the ECM during start-up. Deep cycle batteries limit their output to a constant 12 vdc, for a longer period of time which is great for lighting, refrigerators, televisions, and radios, but engines need the extra boost to get things going. Interstate 1,000 CCA conventional wet batteries for me. Volvo had a bulletin out warning against deep cycle battery use as a primary as strange things were happening when the ECM was seeing less than 13vdc. W

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Thanks for the info, everyone.

Anyone happen to know if the Deka start/deep cycle are OE for Chap on a VP? You got my attention with that service bulletin, Wingnut.

I bought her from a dealer with one season/74hrs on her, last owner was fanatical with upkeep, so I doubt batteries were neglected and changed out that fast...

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That idea about electrical equipment is the biggest killer of electrical equipment.  Out of sight. Out of mind & P M checks.  

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On 5/17/2019 at 8:22 PM, Toddavid said:

Current batteries are 5 year old starting/deep cycle type, group 27, Deka. Couple of cells on one battery look to be marginal using my specific gravity gauge.

Same brand/spec lead acid are a third the cost of AGM.

Why shouldn’t I just buy lead acid replacements?

The battery manufacturer is not specified.

From around 2006, the specification is starting batteries only for the engine due to the potential of voltage affecting the ECU/ECM in odd, inconsistent ways. This coincides with when the ECU/ECM became EVC capable whether or not the “option” was “equipped” on a specific unit (it’s in the “background” no matter what). Fast forward to Gen. V, which started showing up within the 2013/2014 to 2016/2017 window depending on specific engine, AGM.

If you have the motor model number, what’s required can be determined for sure. Likewise, a quick call to the Dealer’s service department should get the answer.

If the two above things are not possible, AGM is the safest path forward. More expensive, but best path forward nonetheless. Plus, if I recall correctly, there was a prior post about electrical oddities on the 2014.

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Aren’t we now talking about two different things?

Starter type vs deep cycle type? Both lead acid and AGM come in those varieties.

I don’t think AGM is a mandate for my engine, but I’m not sure if starter type is required vs deep cycle.

And then there is starter/deep cycle hybrid type, which is already in my boat. Online research shows that type has best of both worlds for a slightly higher cost: ability to maintain voltage under heavy draw (starting) and the ability to be run low without damage (running the stereo on the hook).

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42 minutes ago, Toddavid said:

Aren’t we now talking about two different things?

Starter type vs deep cycle type? Both lead acid and AGM come in those varieties.

I don’t think AGM is a mandate for my engine, but I’m not sure if starter type is required vs deep cycle.

And then there is starter/deep cycle hybrid type, which is already in my boat. Online research shows that type has best of both worlds for a slightly higher cost: ability to maintain voltage under heavy draw (starting) and the ability to be run low without damage (running the stereo on the hook).

Starting type. Whether AGM or not depends. Your 2014 might require it depending on what engine. Post model or call Dealer. 

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3 hours ago, Toddavid said:

V8-380-C-D, serial A254656.

Thank you. AGM is not required.

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Thanks, Curt.

What’s the consensus of using starter/deep cycle hybrid batteries for both? I do like to hang on the hook and play the subwoofer-powered tunes for long hours.

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I see hybrids as coming  up short on both requirements.  Go with the starting battery & a deep cycle for music. 

Does your engine start in 2 seconds or less ?  You can go wit a standard cranking capacity battery.  Take that lower capacity  start battery money & put it into a BIGGER music sized deep cycle battery. Deep cycle batteries will tolerate running them down to lower voltages better.  Weight of a battery USUALLY means longer music time.

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11 minutes ago, Toddavid said:

Thanks, Curt.

What’s the consensus of using starter/deep cycle hybrid batteries for both? I do like to hang on the hook and play the subwoofer-powered tunes for long hours.

You need to use the starting type with that engine. Your ECU/ECM will thank you, and electrical oddities and reliability issues will be avoided. If you are concerned about time on the hook with that audio setup, add a dedicated deep cycle.

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With a factory two battery switch system, any issues using starter in position 1 and deep cycle in position 2?

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13 hours ago, Toddavid said:

With a factory two battery switch system, any issues using starter in position 1 and deep cycle in position 2?

It depends on how its wired, but I believe this is okay.

To confirm, if you’d take and post a picture with both batteries in the frame from above, so they and all of the wiring coming from and among them is clearly visible, that will be very helpful.

Thinking out loud. Unless you’re planning on jamming a straight 8 to 12 + hours without any motoring whatsoever, a proper pair of starting batteries should do just fine. Was_Wylie_Tunes, RJBergen (I may have the handle wrong) and Iggy are the resident audio experts. I defer.

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So I'm jumping into this thread a little late and I'm going to come in from left field. :lol:

Batteries have always been interesting to me, and I studied them a little bit back in my computer engineering undergrad.

I'll start off by saying I'm going to be ignoring Volvo's warning against using deep-cycle batteries on my 2006 5.7GXi-F engines, so take the following how you want. Volvo states in the manual:

Quote

CAUTION! Do not use deep cycle batteries on EFI engines. A deep cycle battery, while it may have enough cold cranking amps (CCA), will cause problems with EFI engines. The correct starting battery for all Volvo Penta EFI engines is a standard marine battery with a minimum of 650 CCA and a minimum of 135 minutes reserve capacity.

That said, I'm going to be installing 3 Duracell AGM Deep Cycle Group 31 this spring. I already have them, but I need to change out the mounting trays.

Let's start with some definitions:

Cold Cranking Amps (0°F)/Marine Cranking Amps (32°F): the number of amps a 12-volt battery can deliver at 0°F for 30 seconds while maintaining a voltage of at least 7.2 volts

Reserve Capacity: how many minutes the battery can deliver a constant current of 25 amps at 80°F without falling below the minimum voltage of 10.5 volts

Amp Hours: the energy a battery can deliver continuously for 20 hours at 80°F without falling below 10.5 volts

Cranking amps are most important for engine starting. It's the measure of surge energy that the battery can deliver. Now, you'll see that the cranking amps rating allows for a minimum voltage of 7.2 volts which is actually rather low and could cause issues with Volvo's EFI system. However, Volvo should have designed their ECM to handle that low voltage as it is a standard in the battery community.

Reserve capacity is most important for high current draw loads like audio amplifiers.

Amp hours are most important for house battery banks where there is likely to be a long-term low current draw powering lights and intermittent devices like refrigerators and bilge pumps.

Here is a chart showing battery voltage vs. charge percentage:

dsc-marine-electrical-systems-seminar-02

As you can see, 10.5 volts is actually a dead battery with nothing left. With batteries, you do not want to discharge below 50% of capacity to achieve the longest cycle life out of it. You'll see that 50% of capacity is 12.06 volts, let's call it 12 volts. Also note, the "After 3 hour rest" at the top. That's because there's a surface charge present that takes a while to dissipate after charging. If you measure battery voltage too soon after charging, you can be tricked into thinking you have a fully charged, healthy battery when in reality that might not be the case.

Reserve capacity and amp hours are related and both measures of how long a battery can supply current until it is fully discharged. Reserve capacity is measured at a constant current of 25 amps while amp hours are measured over constant time of 20 hours. The calculation to find the current that the battery can supply over those 20 hours is simply dividing the amp hour rating by 20 hours and you're left with current measured in amps. It's usually just a couple amps. As current draw increases, battery capacity decreases. Batteries work best supplying low amounts of current for long periods of time.

Now with regards to battery construction types, there are many:

Flooded Lead Acid: this is what most people think of when you say lead acid battery. It is lead plates submerged in liquid sulfuric acid. They have ports on the top and need to occasionally be filled with distilled water. They cannot be installed in any position other than vertical. The lead plates are simply hanging in space inside the battery and are not supported side to side. They are not as resistant to shock and vibration as other constructions. If the battery case is broken, sulfuric acid leaks out.

Absorbed Glass Mat: These are known as AGM and they use a liquid sulfuric acid solution which is soaked into fiberglass mats that separate the lead plates. The plates are all supported by the mats and make the battery very resistant to shock and vibration. Since the electrolyte is absorbed into the mats, they can be installed on their side, but most of them do not allow for inverted installations. They do not require maintenance since the electrolyte is absorbed in the mats. If the battery case is broken, no acid leaks out.

Gel: These batteries use an electrolyte gel in between the lead plates. They are more sensitive to charging profiles than AGM and can not be refilled with distilled water if electrolyte is boiled off. Gel batteries typically don't see much use because they don't offer as much energy density as AGM batteries requiring a physically larger battery for the same energy storage. They are more sensitive to charging and require special voltage regulators if you want to charge with your engine alternator. Gel batteries are perfect for low current draws over very long periods of time. They do not do well with high current draws. If the battery case is broken, no acid will leak out because it is a gel.

The construction style of the battery does have some effect on the battery ratings (CCA/MCA, RC, and Ah), but the construction type does not by itself make a difference with how the batteries are used. It baffles me that manufacturers specify AGM or non-AGM. It literally means nothing and shows they did not have an electrical engineer providing input into the manual. The only things that matters is the actual ratings.

Let's talk starting vs. dual-purpose vs. deep cycle. This is a matter of the internal construction of the battery and relates to how a battery provides current. The chemical reaction that generates electrons, which are measured as current, occurs on the surface of the lead plates. More surface area allows the battery to supply larger amounts of current. As the chemical reaction occurs, the strength of the acid solution in contact with the lead plates decreases which decreases the battery voltage. Given time, the acid solution will diffuse and equal out throughout the battery and the voltage will climb gradually after a high current draw event.

Starting batteries use the thinnest lead plates. This provides the greatest number of individual plates and therefore greatest surface area. This allows for a high current draw for a short period of time. Dual-purpose batteries have thicker lead plates to allow for a deeper discharge, but still supply high current for brief periods. Deep cycle batteries have the thickest, and therefore fewest plates. This allows for excellent deep discharge capabilities, but limits the amount of current it can supply due to plate surface area.

And now I'll circle back to how you can theoretically use any battery to start an engine as long as it meets the specifications. Starting an engine requires a certain number of CCA or MCA depending on the starter and the size of the engine. The manufacturer should specify how many CCA are required. In the case of my 2006 5.7 GXi-F, that is 650 CCA. The AGM deep cycle batteries I'm installing are rated for 800 CCA, or 123% of Volvo's requirement. That said, I am increasing the size of my batteries from Group 27 to Group 31. Had I not done that, the group 27 AGM deep cycle can only supply 580 CCA and they don't make an AGM starting battery. The group 27 flooded lead acid starting battery can supply 840 CCA and the same size dual-purpose battery can supply exactly 650 CCA.

I think the largest issue, and why the engine manufacturers make so many statements, is that people simply replace their existing batteries with the same size. That causes trouble when you replace a suitable starting battery with an equivalently physically sized deep cycle which now cannot produce sufficient starting current and causes a low voltage situation for the ECMs. If you pay attention to battery specifications and ratings, you can use any battery that meets the electrical needs of the application you'll be using it for.

Sorry for the long post, but feel free to ask questions.

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Good news about electrons in all batteries.

THEY ARE ALL THE SAME.  Size shape  and strength.     You could use enough D size flashlight cells to start a Volvo.   Volvo is selling fear.

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28 minutes ago, cyclops2 said:

Good news about electrons in all batteries.

THEY ARE ALL THE SAME.  Size shape  and strength.     You could use enough D size flashlight cells to start a Volvo.   Volvo is selling fear.

This basically summarizes my post. If your battery can provide enough electrons, it will start the engine. 

Volvo instills fear by saying a deep cycle will damage your engine. In reality, low voltage will damage your engine. That low voltage is caused by replacing the stock flooded lead acid starting battery with a flooded lead acid deep cycle battery of the same size, and fewer CCA causing a quicker drop in voltage while starting. The fix is to ensure the battery you use can supply 650+ CCA and that can be achieved with a deep cycle by increasing the group size  

I believe the Mercury Verado outboards state they require an AGM. Again, just like Volvo, a flooded lead acid battery with sufficient CCA will not damage the engine. They instill fear by requiring an AGM to provide sufficient CCA. Most AGMs have higher CCA than a flooded lead acid of equivalent physical size and use (starting/ dual-purpose/deep cycle). Same as I said about Volvo, you can use a flooded lead acid with Verados as long as it provides enough CCA and that likely means increasing the group size over the AGM. 

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16 hours ago, Toddavid said:

With a factory two battery switch system, any issues using starter in position 1 and deep cycle in position 2?

That's how mine is configured. 

 

I buy all my batteries at Costco ( Interstate Starting and Deep Cycle Marine ) and return them just before the free replacement period expires. They do not have the ability to test them and simply give you a new one. I always have fresh batteries and have not had to pay for one in years. 

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1 hour ago, rjbergen said:

Sorry for the long post, but feel free to ask questions.

Why apologize?  That was an awesome post.  The only thing you didn't mention was what is the CCA for a Groupe 31 dual purpose AGM?  That's what I changed all my batteries to and they work and charge great, whether by alternator or battery chargery/shore power.

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I run an Interstate starting battery and an AGM dual purpose as my "house" battery.  When I'm on the hook, I switch over to the AGM.

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15 minutes ago, Hatem said:

Why apologize?  That was an awesome post.  The only thing you didn't mention was what is the CCA for a Groupe 31 dual purpose AGM?  That's what I changed all my batteries to and they work and charge great, whether by alternator or battery chargery/shore power.

I'm not sure how many CCA you'd have. I only have the Duracell AGM datasheet right now and they don't have a group 31 dual purpose AGM.

What brand do you have?

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