AGM in older car

Messages
21
Location
North east
Need to buy a new battery for my 1968 Plymouth with 440 engine, is there any problem going with AGM battery? I like the idea of it being sealed but have read AGM's require different charging requirements and may be overheated by overcharging in an older cars charging system. TIA
 
Messages
300
Location
SE Michigan
AGM batteries don't like to be charged anything past 15 volts. Cars that were originally equipped with them almost always have smart charging systems that take that into account and won't hit them with really high voltage. For older cars without "smart" systems voltage goes up as temperature goes down. I'm doubting that you drive your 60's muscle car in January, so you might be OK. Have you got a voltage gauge already? I love the toughness, indifference to mounting, and reduced maintenance of AGM, but I'd be careful about the application. I have one in my boat, but the outboard has a small charging system that couldn't hit 15 volts if it tried, and I only run it in the summer. I've specifically told the parts guy NOT to give me an AGM on a car that wasn't originally equipped with it because I've seen the charging system hit high voltage in the cold.
 
Messages
1,873
Location
New England, USA
I have gone to AGM's for everything in my sig, including the airplane as of this weekend, except the Lotus (none available). I find they last longer on seldom used cars, self discharge less and don't leak or produce as much crud as flooded batteries. While they have lasted longer for me, they may still not be cost effective, but that is not my primary concern. I have had no problems with their charging in my primitive cars. Assuming you have a good alternator, you should be fine. I'm not sure I would try one with a generator without doing some research.
 
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36,409
Location
ME
They make adjustable external voltage regulators for Mopars. Should not be a problem picking a voltage that works for you and your battery chemistry. My Prius rolls at a low-ish 14.0 V summer or winter, with its trunk-mounted battery. I have an AGM in there, basically because it was cheaper (!), fit, and the OE 12v lead acid batteries are lame.
 
Messages
900
Location
New Hampshire USA
Have an AGM in my 77 in my sig. on third year now and found it at 50% second year now, never had this with all previous bats. It does sit in a cold garage which goes below 0 and I leave it be all winter. Otherwise like the fast cranking.
 
Messages
3,173
Location
Western S.C.
Originally Posted by eljefino
My Prius rolls at a low-ish 14.0 V summer or winter, with its trunk-mounted battery. I have an AGM in there, basically because it was cheaper (!), fit, and the OE 12v lead acid batteries are lame.
The OE battery was AGM, too. Depending on circumstances, voltage of my 2011 (3rd generation) alternates between about 14.7 and about 13.7 volts---14.7 when it's cold, or the lights are on, or the transmission is in Park, or the car has just been started.
 
Messages
2,205
Location
california
AGM self discharge less, but when they are discharged deeply, require that they be returned to a full 100% state of charge, to get good longevity, and the deeper they are discharged, the more amperage they should be allowed to feed upon. Deeply discharged AGMs can, and are, tickled to death by low amperage charging sources. They should get no less than 20 amps per 100 Amp hours of capacity when dischrged to 50%. In general the largest 12v battery rwhich might be found in some trucks are a group 31 and these are usually in the 100 amp hour range, meaining it can support a 5 amp load for 20 hours before is voltage falls to 10.5v, which is considered fully discharged. The group 65AGM battery is about 85 amp hours, group 24 similar, and group 27 can be in the 100 range too, these 4 group sizes are generally the largest 12v batteries one will find underhood on bigger engined vehicles. They should be brought to 14.4 to 14.7v, assuming a battery temperature around 77F. colder temps require higher voltages, hotter battery temps should have lower voltages allowed. 15v is not some threshold which instantly destroys the AGM battery, and the cold AGm battery should be brough to and exceed 15v when charging. They ( the Lead acid battery discharged to 50%) will take no less than 3.5 hours after a 20% charge rate gets them to these voltages ,easured at theh battery terminals, before they will be near fully charged. Full charge on an AGM can ONLY be determined when the amperage required to maintain these higher absoprtion voltages tapers to 0.5% of the capacity, meaning 0.5 amps for a 100Ah group 31 battery. Smart chaagers guess, and throw the green light, drop to float voltages, and mock the human who believes it. Haw hawwwww. Some are better than others. Reversion to a float voltage and the soothing green light, does not mean the battery is full, nor does charging stop at float voltage, it just slows down a very significant degree and while a healthy battery will eventually reach full charge at float voltage, an unhealthy battery will not. The lesser the depth of discharge, the less important it is to approach/achieve this Ideal recharge regimen. Do not listen to those that say to trickle charge deeply discharged AGMS. They respond incredibly well to higher amp recharges, and Odyssey's reconditioning procedure says to discharge to 10v under a fairly high load, then immediately apply no less than 40 amps per 100AH of capacity until 14.7v is reached, and hold until amperage tapers to near Zero. lather rinse repeat if required. Concorde AGM, who malke Mil spec AGm batteries, one of their brands being Lifeline, say to normally fully charge( meaning hold them at 14.2 rto 14.6v until amperage tapers to 0.5% of capacity( 20 hr rate), and then bring them to and hold them at 15.5 volts for 8 hours as their recommended reconditioning procedure . If AGMS are deeply discharged, and not recharged at a fairly high rate, to a true full state of charge, they will not have a good lifespan. This is pretty much a guarantee, but it is pretty amazing how much CCA they can still provide when seriously capacity compromised, and near fully charged to near that remining potential While many alternators have internal Voltage regulattion, others do not. Most alternators will have NO issue achieving a 40% charge rate on a deeply discharged battery, IF and only IF the voltage regulator not only seeks mid to high 14 volts, but also holds that higher voltage for a good period of time and ideally, until the battery is full, or gets too hot, which is a possibility when high amp recharging. Getting any healthy lead acid battery that is 80% charged, from 80% to 100% takes no less than 3.5 hours. This is a simple fact, and higher voltages, over 14.7ish volts, cannot safely take any significant time off this fact. If the battery is less than healthy 80% to 100% takes even longer. If these higher voltages (14.4 to 14.7) are not held for longer, the unhealthy well discharged battery starts looking for the nearest cliff to dive over. Almost NO Vehicle, even if driven for these 3.5 hours, will hold mid to high 14 volts, and 1/2 to 1/3 the amps flow at 13.7 compared to 14.7v. Many people assume the voltage they see after starting the engine is the voltage the vehicle always holds. This assumption is unwise in the extreme. All lead acid batteries wish to always be fully charged, and kept cool. Anything less than this ideal, compromises their potential longevity, to some degree. The lower their average state of charge, the more they are negatively affected the higher their average temperature the more negatively they are effected. Cold temperatures slow down self discharge, and will not damage a fully charged battery, but cold temperatures reduce CCA and capacity and will reveal a compromised battery. Heat is the cumulative killer, but cold is the revealer. Since the vast majority of people, even very qualified mechanics, seem to assume the alternator is some magical battery charger that can defy those 3.5 hours from 80% to 100%, most batteries intentionaly or unintentionally discharged a fair degree, remain in a constant state of undercharge. This seems to affect AGM batteries more than wet/sloshy/flooded lead acid batteries, and one gets to pay more for the privilage of a battery that is less tolerant of chronic undercharging abuse. But if one can indeed recharge promptly to full 100% state of charge, and to full charge at a high rate when deeply discharged, then one can achieve almost ridiculous lifespans from a quality AGM, or a deep cycle flooded battery. Starting flooded batteries are never going to be happy for long in deeper cycle duty even if recharger ideally and promptly to full. AGMs blur that line between deep cycle and starting, and flooded marine batteries have little in common with flooded deep cycle batteries, despite the deep cycle claims on the sticker. I am on 5.5 years on a Northstar AGM battery. That by itself is no great accomplishment, until one factors in the fact that it has no less than 1100 deep cycles on it, many hundred of those cycles down to 35% charged several dozen to the 20% charged range. If I cound not promptly and truly fully charge this battery, at a high rate when deeply discharged. It would have been recycled long ago and I could join the legions who blame the battery for my ignorance in its proper care and feeding. Blame the vehicle's or charger's voltage regulation. Blame ignorance of the 3.5 hour rule from 80% to 100% state of charge rule. Most vehicles do not, will not have ideal battery charging voltages for good battery longevity. Ideally ones vehicle would bring system voltage upto mid 14's until the battery was indeed truly full, then settle in the mid 13's once full. Almost No vehicle does this. If the battery is never discharged much at all, then the battery does not need 'ideal' to live well beyond the warranty. If the Lead acid battery is discharged regularly, well below 100%, and lives perpetually in this undercharged state, it will be lucky to last the warranty period. Maintenance minded Bitogers seeking good battery longevity should regularly charge the battery overnight on a charger capable of bringing the battery to the mid 14's for a few hours, but any charger is better than no charger. Low rate' trickle' chrgers might not have enough time overnight to get the battery to the mid 14's, much less hold them there for a few hours. If one inadvertently drains their battery to the point it needs a jump start, the battery should be put on a charger immediately once one gets home, but surface charge from the alternator might trick many smart chargers and they will all too quickly revert to float voltage. Knock off the surfacee charge voltage with the headlamps for a few minutes( drop voltage below 12.5 or so), then hook up and start the charger, then turn off the headlamps. Ther person who believes the drive home after a jumpstart was required, even if it is 4 hour drive, was enough to fully charge the battery, is seriously deluded. If the voltage regulator is seeking and holding voltages in the mid 14's( which is quite rare), the jumpstarted battrey can be returned to 80% state of charge fairly quickly perhaps as little as 30 minutes, but That depends on the ability of the alternator to not only power the vehicles electrical needs, but have plenty of excess amperage producing capability to feed the depleted battery at a high amperage rate. It also depends on teh health of the battery. an unhealthy battery can be brought up to higher voltage quicker with less amperage required, where a healthy battery's voltage will rise slower with higher amperage applied. And there is no getting aroud that 3.5 hours minimum( often much longer) to get from 80% to 100% state of charge, not even if you have a 300 amp chromed alternator you just polished while telling it how pretty it is. Don't fear AGMs in older vehicles or vehicles that did not come with them, although you might not get any advantage from them. their charging voltages ar elargely the same as wet/flooded batteries despite what one reads parrotted over and over on the internet that says the opposite Dont fear high rate recharging, unless ambient temperatures are quite high, which underhood at slower speeds, they could certainly be. An AGM is not killed instantly if the vents should open. It takes a lot to actually pop the vents, and would require high amperages applied from a low state of charge, at high ambient temperatures for this to occur, and it would have to occur often and regularly for it to actually 'dry out' an AGM. If the battery is nearly fully charged, it cannot accept high amperages, and high voltages are extremely likely to pop the vets and 'dry out' the AGM. But I have to keep in mind 'AGM' is the new battery marketing buzzword, and they are getting cheaper and cheaper. These mass marketed lower priced AGMS are likely cutting a lot of corners for maximum profit. They should be fine in most instances unless they are regularly deeply discharged and they bake underhood while the voltage regulation is seeking high voltages and the dutiful and capable alternator has no issues providing high amperage to the battery, over and above what the vehicle needs to run its electrics, for a good period of time.
 
Messages
1,873
Location
New England, USA
wrcsixeight, you make a great point, thank you. My post should read: "I have gone to <span style="font-style: italic"><span style="font-weight: bold">quality</span></span> AGM's..." Reputations for quality evolve, e.g. Optima, so do some research on brands.
 
Messages
474
Location
CT
Unless you upgraded to a solid state voltage regulator I wouldn't go AGM. The mechanical points ones on the 69 and older mopars where kinda crude. And the round back single field wire alternators are only 60amp flat out. At idle they aren't doing much.
 
Messages
2,169
Location
Massachusetts
In my experience using AGMs and wet cell batteries in my motorcycle the AGMs did not last as long as the wet batteries, probably due to the abuse they get. Factor in the price difference, and I would rather replace the wet cell every couple of years instead of hoping the AGM will give me 4 years. Bottom line: wet cell traditional batteries have theoretically shorter lifespans, but in practice tolerate abuse much better and cost a lot less up front. In the worst case scenario you kill the battery it is nice to know you can easily replace it cheaply and easily at a Walmart or auto parts store. On the other hand, if like wrcsixeight you know what you are doing and carefully monitor things, you can get great service out of AGMs.
 
Messages
2,235
Location
SE MI
We deal with hundreds of thousands of vehicle batteries, and the AGM's simply last longer in hot environments. However, the alternator regulator has to be designed to charge AGMs, otherwise it will never fully charge up an AGM battery. I'm not sure if the latest Ford ECUs can accomodate AGMs, but there are changeable options using FORScan to set the type of battery (flooded wet cell, etc), so I am assuming the ECU has different charging profiles to send over to the regulator.
 
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13,017
Location
Indiana
Rather than starting a new thread, I feel this would be better off asked here.

If indeed an older electrical system can’t fully charge an AGM, could this be countered by using a battery tender when the battery isn’t in use?
 
Messages
2,696
Location
San Rafael, CA
I've successfully used AGM batteries in vehicles that didn't come with AGM.

I also have a couple large AGMs in my home for if the power goes out. One is a Super Start Marine with a big pure sine wave inverter for my kitchen appliances and fridge one is an Odyssey Extreme that I hacked into my CyberPower UPS for my network.
 
Messages
469
Location
Cheshire, England
wrcsixeight,

Do your comments about the charging requirements of an AGM differ when applied to a Gel/AGM hybrid battery. I have one in my 40 year old motorcycle with the regulator adjusted to 14.5 volts cold. It seem to hold it's charge incredibly well and if I do put a regulated but manual charger on it also set to 14.5 volts, the charge current drops to near zero in a matter of minutes. It's never to my knowledge been deeply discharged and shows no changes in behaviour coming up to 7 years old. I'm wondering if the VR could be set a couple of tenths higher given the manufacturers data sheet.

The data sheet calls for:

Float charging voltage @ 25 C 13.60 to 13.80 V

Cyclic charging voltage @ 25 C 14.50 to 14.9 V
 

JHZR2

Staff member
Messages
45,967
Location
New Jersey
Rather than starting a new thread, I feel this would be better off asked here.

If indeed an older electrical system can’t fully charge an AGM, could this be countered by using a battery tender when the battery isn’t in use?

Yes. I have significant experience doing this.

My 91 BMW never had the voltage I preferred. This is common with old euro vehicles, my old MB cars are worse. To add to that, the BMW had the battery in the trunk.

I put a group 49 AGM (Deka) in there and ran it for years, no issues. I’d top up occasionally. Never an issue. Drove that car everywhere and counted on it for work travel. 5+ years with that AGM never getting a proper charge from the car.

My old MB diesels will potentially get AGM batteries as they need replacement, simply because Costco has German made AGM for a reasonable price. Those cars have even lower alternator output/voltage.
 
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