Originally Posted by wrcsixeight
Regarding charge profiles and the differences between AGM and flooded,
They are not really consequential when the battery is used as a starting battery.
When the battery is cycled deeper, then meeting the manufacturer recommended charge profiles become more important, but a shallowly cycled AGM used as a starting battery will be fine with the voltages allowed by the vehicle, as they are hardly ideal and made for ultimate battery longevity to begin with.
The biggest difference in charge profiles spec'd by manufactures is float voltage.
Float is a battery charging stage designed to keep the fully charged battery, fully charged, without overcharging.
Float voltage specs for flooded batteries range from 13.01 to 13.4 volts
Float voltage specs for AGMS range from 13.4 to 13.8v
All assume a 77f battery temperature.
Almost no vehicle with a properly working charging system allows less than 13.6v anyway, so the float voltage spec is ignorable in this application. There re exceptions to the 13.6v as some vehicles want to keep the battery discharged enough that it can accept higher amperage from teh alternator when teh computer controlled voltage regulator commands it to bring system voltage into the 14's. Some manufacturers do this to eek out a few hundredths of a MPG as it is said every 25 amps the alternator has to produce sucks up one engine HP.
Absorption voltage, which is basically the maximum voltage the manufacturers will recommend for both, range from 14.2 to 14.9v depending on the manufacturer.
A bigger difference with AGMS appears when they are deeply discharged. A 100AH AGM should receive no less than 20 amps and should be brought upto absorption voltage with this much current and held there until it is fully charged some 4 to 5 hours later. Since few are driving for that long anyway it makes little difference. Some of the le$$er AGMS will say apply no more than 30 or 33.3 amps per 100Ah of capacity when deeply cycled.
In the case of a unintentionally discharged battery, the alternator, after a jumpstart will exceed this 33% charge rate by a huge factor. No mushroom clouds!! Hmmmmmmm.
NOw some vehicles will allow voltages over 15. In general AGMS should not be brought up this high regularly, but if they are already close to being fully charged, they will not accept much amperage and it is unlikely they will pop their vents, and popping the vents is not instant death anyway
A Deeply discharged AGM fed high current upto a high voltage grater than 15, is much more likely to pop the vents, especially if it is in a hot engine compartement and itself gets quite hot not only from this ambient heat but the heat from high amperage charging,
Once cannot add water to AGMS, but it is unlikely that AGMS will dry out anyway, before they time out, or cycle out of service.
What an AGM can do, when well depleted, is potentialy overheat the alternator. Due to their lesser resistance, and when below 80% charged thay can accept much higher charging currents than their equal sized flooded counterpart.
But since the most vehicles will not be seeking to hold mid 14 volts for very long before reverting to mid to high 13's i is unlikely the alternator will overheat, as voltage is electrical pressure, and less pressure means less amperage flow, this too is unlikely to occur.
So by and large, the whole' do no put an AGM in a car designed for flooded' is hogwash.
Whther the ability tof AGM to accept more current at the same voltage, compared to flooded, is indeed benefical is argueable.
Whether their higher CCA is of benefit, and worth the added cost, is argueable.
Whether their lack of terminal corrosion is worth it is.. argueable.
Whether their much lower self discharge is beneficial is argueable.
AGMS can likely still start a car when well discharged in low temperatures, where their flooded counterpart discharged the same % could not, again the benefits are argueable, nd all depend on the application, the climate and the vehicles usage.
RV and Marine users of AGMs report that they are less tolerant of never receiving a 100% true full charge in deep cycle duty.
A daily driver cannot be considered deep cycle duty, but sitting for 3 weeks on a modern vehicle with their larger parasitic loads, is basically depleting the battery to the 50% range, and that is indeed a deep cycle.
In such a case the alternator is not being allowed to seek and hold the higher voltages either battery desires, but the AGM battery will accept higher amperages than the flooded, and reach a higher state of charge in teh time the vehicle is driven, all other factors being equal. The AGM might degrade a bit faster if it is not brought to a true full charge, whereas a flooded battery might be less stressed by this abuse.
In deep cycle service, the marine dual purpose battery or the deep cycle battery can have an Equalization charger performed, a forced extended overchargevwhich can revert the capacity loss caused by chronic undercharing. No AGm manufacturer documentation( but for Concorde/Lifeline) allows for an Equalization charge to be performed, and they limit voltage to 15.5v, where most flooded deep cycle batteries allow 16.2v during this forced overcharge.
Just remember all lead acid batteries would ideally prefer toalways be fully charged, and kept cool, for maximum longevity and performance an reliability during that longevity. They ideally always want to be promptly returned to full charge anytime they are discharged. they despise sitting in an undercharged state. No Lead acid battery is immune to this, though there are some newer plate pastes containing carbon said to be much mroe tolerant of Partial State of Charge cycling, PSOC. By and large these 'enhanced' batteries have not made it into the automotive starting battrey market, especially in the US.
No vehicle charging system is concerned with battery longevity and achieving ideal recharging. It is much safer to shoot for not overcharging so the voltages allowed are timid at best, and far from ideal and charging from 80% to 100% still takes no less than 3.5 hours at ideal chrging voltages, Ideal charging voltages rarely being held anyway.
AGM has become the battery Buzzword. Manufacturers smell more profit, and consumers are cheaper than ever.
If the AGM you are considering appears to have a great price, and does not have a considerably higher CCA rating than its flooded counterpart of the same size group, then its internal resistance is not much lower either, eliminating many of the AGM benefits, but for the terminal corrosion.
And AGMS can still grow green and white corosion on the terminals, but of course to a much lesser degree than flooded batteries.
Seeing the considerable price reduction of the latest AGMS seen here on Bitog, other sites, and in AP stores, makes me wonder just how many corners manufacturers have cut to produce and market these desirably priced AGM's.
The Best AGMS by Concorde, Odyssey and Northstar, their prices have not budged. These high $$ AGMS have the lowest resistance, the highest CCA figures, the lowest self discharge numbers, and if properly recharged can deliver exceedingly impressive performance in deep cycle/dual purpose applications. If they are not properly recharged in such duty, then they will last little longer than the cheapest AGM, but do stand a better chance of recovery, should one have the equipment and ability and desire to perform the recovery procedures.
Lifeline says when deeply discharged that no less than 20 amps per 100Ah of capacity is acceptable, and more is better, always, voltage limited to 14.6v max at 77f.
Odyssey says that when deeply discharged, that no less than 40 amps per 100Ah of capacity is acceptable, and once 14.7v is reached( at 77f) hold that voltage for 4 more hours.
So No alternator is going to achieve this anyway, not the 4 hour part i n99.9% of cases, the time it takes for amperage to taper to very low levels where the battery can be considered fully charged or close to it. Neither is it likely the vehicles voltage regulator seek or hold the higher voltages required for the time it takes to bring the battery back to 100% full charge.
The flooded battery could indeed be more tolerant of not being fully charged, than its AGM counterpart making the more expensive battery a questionable choice, in a vehicle that came with a flooded battery.
In most cases Flooded batteries should not be used in vehicles that came from teh factory with AGM's. AGMS do not offgas unless they are overcharged, but a flooded battery has to offgas to reach full charge, and will offgass in the ~85% and higher charged range when held at ~14.2v or higher. The hydrogen and oxygen are flammable and when they leave the battery they take some sulfuric acid mist with them, which is a carcinogen if breathed regularly in high enough quantities. If the vehicle came with an AGM placed in the trunk or in the passenger compartment, do not replace it with flooded battery.
Gassing of flooded batteries only occurs at higher voltages at hihger states of charge in most cases, so the whole 1960's VW beetle battery being below the seat and being 'just fine' and not killing people, is no longer a legitimate arguement why it is just fine to do the same in a modern vehicle.
AGMs can be used in most every vehicle which originally came with a flooded battery, but it might not be beneficial at all, except in the terminal corrosion/regular watering department.
AGMS can be a bit of a princess battery. No Lead acid battery likes being chronically undercharged, but the princess might throw a tantrum sooner should it be asked to work hard, and not get what it wants regarding recharging. The husband would be wise to make it happy with a regular full charge, despite the 'low maintenance/no maintenance' marketing they believed.
wrcsixeight - wow, thank you for the very detailed response. I learned a lot from your post.
Originally Posted by bbhero
Got that right man...
I thought to myself I must be living right
Quick question... What do you think of the Napa maxdrive CV axles?? They claim they are "new"... I am going to replace my left side CV axle coming up.. and I'm thinking of getting this one vs the stuff from AZ or AAP.
They are all made by Cardone anyway. Pick the cheapest one with the easiest exchange. My luck with any "new" aftermarket axle has been extremely poor. I suggest getting a reman from CVJAxles; they build using OEM cores. Their pricing is not much more than the "new" axles...probably around $150-$175 once you include the cost of 2-way shipping.