There is no proof that there is anything wrong with your battery(s).
Smart chargers are not really smart. They largely follow a one size fits all algorithm, and the rest of the effort is expended in extra special marketing claiming how great they are.
On this forum, like many products, they are given godlike status with no proof whatsoever that they do what they claim to do.
The lead acid battery lives it longest life when it is truly fully charged and kept cool.
There is a huge difference between good enough/charged enough to start the engine, and truly fully charged.
TPPL Agms like Northstar and Odyssey are impressive batteries, huge CCA numbers and can gobble up as much amperage as you likely can muster,/ throw at them, just limit the voltage to 14.8v and reduce this voltage the hotter the battery is over 77f/25c.
TPPL AGMs can also be deeply cycled, but when deeply cycled, they need the high amp recharge from their most depleted state, perhaps not each and every deep cycle, but at least once every 6 or 7 deep cycles. If they do not get this they will lose their ability to perform, and without the true full recharge this loss of capacity and performance only increases its rate. It is unlikely this lost performance can be recovered, but by all means try, just don't expect stage 8 super fellate smart charger's ' reconditioning cycle' means the battery is actually improved, especially if one does not know how high the voltage got, how much amperage the battery accepted at those voltages, and how long the elevated voltages were held.
By and large a smart chargers green light only means the battery is charged enough to start he vehicle and or that the battery charger has stopped charging at voltages above float. it does not mean the battery is truly fully charged.
I've fed my group 31 northstar (103ah capacity) as much as 134 amps when it was depleted to ~40% state of charge.
Lesser, cheaper AGMS will say to limit charge amperage to 27 to 33 amps per 100 amp hours of capacity.
The Deka Intimidator is likely the most rebranded AGM battery available, and a Bitog favorite. It will say to limit charging current to C/3, which is 1/3 the amp hour capacity rating or 33 amps for an ~ 100 amp hour group 27.
It could be a perfectly good AGm for dedicated engine starting, with the rare deep cycle here and there, but in deep cycle usage it falls well short of the other higher $$ agms in performance retainment, even when promptly and properly recharged.
The Deka intimidator says to limit to 30 amps per 100Ah of capacity. I have a 5 year old pair of Deka intimidator golf cart batteries at 190 amp hours capacity.
According to Deka, do not charge them at more than 57 amps. yet They will still easily accept 120 amps when discharged to the 50% range, and do not heat excessively when I do this, and they still perform well.
Odyssey AGM outright states no less than a 0.4C charge rate in deep cycle use, meaning no less than 40 amps for their 100 amp hour group 31.
Lifeline AGM, which is pretty much top dog deep cycle AGM also states the more charging amperage, the better, page 20 in the link below.
I've found Northstar documantation to be lacking, and always followed Odyssey recommendations.
When I spoke to an odyssey engineer a while back he was adamant that if the long term float voltage applied from a float or maintenance charger was not 13.6v, at 77f, then it should not be floated long term. Lots of so called 'maintenance' charger will float at 13.2, even on the AGM setting. Floating at too low a voltage for a long time is not a good thing, but especially when there is a significant parasitic load on the DC system.
Floating too high a voltage is overcharging and causes positive plate degradation and flooded batteries will use a lot more water.
On my own system:
If I float my Northstar at 13.6v exactly in the 70f temp range, then crank voltage to 14.8, amps quickly taper to 0.5 or less, usually much less, indicating this float voltage kept the battery truly fully charged.
If I float it at 13.5v in the same temp range, for a day or 2, then crank voltage upto 14.8v, amps will go up above 5 and over 25 minutes taper to the 0.5 range and take another half hour to taper to 0.2. This indicates the 0.1v float voltage difference, allowed the battery to discharge slightly, also proving just how important the float voltage be right for the specific battery.
Note than some AGMs say 13.2 to 13.4 float, others are 13.6 and I think I even saw one was 13.8v all at 77f/25c degrees.
So even if a smart charger has a specific setting for AGM, if the float voltage it holds is too low, the battery can very slowly discharge, even if this float voltage is well above its natural full charge open circuit resting voltage, which on a Northstar is 13.06 in my experience, My Dekas AGMs are about 12.84v.
By and large the smart chargers are given an efficacy rating by users reviewers, that they do not deserve, by those with little to no ability to actually make any judgements as to performance/ efficacy of the charger.
Ideal lead acid battery recharging can be taken to ridiculous extremes. The deeper the battery is cycled, the more important the charging regimen becomes, and the 95% charged battery needing a top up, is far different than teh same battery cycled 6 nights a week to 50% range but only recharged to 95%, and then on day 6 tries for 100%, as on Day 6 it will take many many hours longer.
Not being familiar with your charger, I will guess that it is expecting the amperage it is feeding the battery at absorption voltage, is not tapering to low levels. A new healthy Northstar held at 14.7v, will have amperage eventually taper to 0.05 or less. When my Group 27 Northstar was obviously at near end of life, the amps would not taper to 0.4 @ 14.7, but would stop tapering, then start rising again as the battery started heating. At first the bottom bounce was 0.5 amps, and over 5 months it would only taper to 1.1 amps before amperage started rising again. Voltage was also falling lower and lower each engine start even when fully charged, and when it was falling to 7.73, it would actually stop cranking for a bit, then keep going at which point the engine would catch. This is bad for the starter.
If a smart charger was waiting for amps to taper to say 0.5, but the worn out, or perhaps sulfated ( from chronic undercharging) battery, but amps never tapered to this level, it might just say 75% and never go higher and even might just shut off.
Remember, the smart charger's job is ultimately, max profit. A huge part of that is to not overcharge a battery, which can be unsafe due to excessive offgassing or thermal runaway. It is much safer to undercharge a battery, and indeed truly fully charging a battery requires more than a simple one size fits enough algorithm. Easiest of all is a bright green light and extra special marketing, and hope the consumer does not have the ability to actually determine true full charge.
If you wanted to test the performance of your vehicle, you'd want to know 0 to 60 times, and similar.
Equate this to the battery's ability to maintain voltage when powering the starter. The cold cranking amp rating. Turn the key and the starter draws ~ 180 amps. A healthy battery will be able to maintain 11+ volts powering this for a few seconds. A weaker, nearer end of life battery will be falling below 9 volts powering this same load for the same duration.
If you wanted to test the remaining capacity of a battery, this can be equated to the size of the size of the gas tank of the vehicle.
When new, the gas tank might be able to hold 20 gallons giving one a 500 mile range on the interstate, but when the battery is older and sulfated the 'gas' tank will still look like it holds 20 gallons, but is actually partially filled with acquarium gravel( sulfated) , and only able to store 12 gallons, and the vehicle range is now only ~ 280 miles all factors being equal.
So in order to check ones 0 to 60 times( remaining CCA), measure how much voltage the battery is able to maintain when starting the cold engine. Or use a carbon pile load tester.
To measure how far one can actually drive on a tankful, one needs to fill their tank, drive a steady speed and see how far it goes.
The 100 amp hour battery, when newish, healthy and fully charged, should be able to power a 5 amp load for 20 hours before the voltage falls to 10.5v, which is considered 100% discharged. It it can only power that 5 amp load for 10 hours before voltage falls to 10.5v the battery has only 50% of its original capacity remaining.
The battery at 50% capacity remaining, might still easily be able to start an engine, but the same battery being deeply cycled would likely not be able to stre enough energy to be used just as hard as it did when new. The 50% capacity battery in deep cycle usage would scream 'INADEQUATE!!" to the user watching their voltmeter during discharge, but the 50% battery as a starting battery likely still easily starts the engine, until it gets really cold out.
In general when capacity decreases to 80% of when new, the battery is recommended to be replaced as the risk of sudden failure after this point raises significantly.
when 100% discharged, the flooded lead acid or AGm lead acid battery will require no less than 102% of the energy removed from it, in order to be returned to 100%. As the battery ages this increases to 110%, then 115% and just gets worse and worse.
When recharging to full, one needs to be able to determine when full charge has occurred. With Flooded batteries with removable caps, a hydrometer dipped into the cells will show when specific gravity reaches previously established maximums, generally in the 1.275 range, but with an AGM, the ONLY way to be sure when full charge has been achieved, is by watching the amperage taper, when the battery is held at 14.4 to 14.8 volts. Lifeline states when held at 14.4v when a 100 amp hour battery can only accept 0.5 amps, it can be considered fully charged.
This is a good threshold, but perhaps on Odyssey or Northstar which are thin plate pure lead vs Lifelines much thicker plates, one should wait until it tapers to 0.2 amps per 100Ah of capacity instead. These TPPl agms will likely taper to less than 0.05 amps when new, but it could be unnecessarily abusive to get from perhaps 99.993% to 99.999%. The extra 0.007% can be achieved at float voltage, over 8+ additional hours.
Again, when an AGM battery is never really worked hard, and especially with these TPPL agms, when they do not get to stretch their legs/ lungs, they get all petulant. They are like an unexercised thoroughbred. Top charging is good ovbiously better than being kept at 80%, but really a petulant AGM needs its version of an italian tune up. Deplete it to 12.1v or less with a relatively large load, like the headlamps left on 10 to 15 amps) and measure how long this takes, then immediately feed it no less than 25 amps until it reaches 14.4 to 14.8v, then hold it at 14.4 to 14.8v until it tapers to the 0.3 amp range. Never discharge to less than 10.5v under lesser loads like headlamps, and never intentionally leave a discharged battery to sit in a well depleted state.
If ones plug in charging sources are well short of 25 amps, then the alternator can easily exceed this, but the voltgae regulation will likely back off from 14.4v and voltage being pressure, lesser pressure means less flow. I'd reccomend against idling to high amp recharge a well depleted battery, get on teh freeway, underhood airflow is important as is rpm above idle at keeping alternator from overheating.
If one really cant ever muster high amperage to recharge a well depleted AGM, The Lifeline link below on page 20 has a 'constant current' recommendation stage which is supposed to offset the degradation caused by deep cycling followed by less than a 0.2c charge rate, 20 amps per 100ah of capacity. They basically say apply 2 amps at the end of the 'normal' charge cycle for 2 hours and do not mention how high this 2 amps will push the voltage, but I will guess from experience it is well into the 16's.
please keep in mind Lifeline/Concorde AGM is the only AGm manufacturer which says anything about allowing voltages over 15.
charging a AGM from 50% to 100% is likely 6.5 hours minimum on a healthy battery, and 10+ hours on a mid life battery, and 13 hours or more on an end of life battery, before amps taper to the prescribed level when held at absorption voltage, which determines when the AGM can be considered full.
If you dropped off your Northstars, I'd hold them at 14.7v until amps taper to 0.3 amps, then use it hard over about 4 to 6 hours, until voltage fell to the 12.05 to 12.2v range with about a 6 to 10 amp load, which would have the battery somewhere in teh 50% charged range.
then I'd hook it up to my 100 amp power supply set to 14.7v.
I'd judge its condition by how much of that 100 amps it can accept, and how long it takes those 100 amps to raise voltage at battery terminals to 14.8v.
I'd also judge its condition by how long it takes amps to taper to 0.3.
I'd also hope that the amp hour counter on my charger output, when those amps taper to 0.3 at 14.7v, counted somewhere close to the original stated capacity.
I'd also run an IR thermal gun over each cell while charging and see if any one cell or bottom of a cell got significantly hotter than the other 5.
This particular deep cycle/high amp recharge/ amp hour counting method, if done back to back, tends to have the battery improve its capacity. I can and do go below the 50% state of charge boogeyman, and the longer the battery can accept higher amperage the more likely the heating caused by high rate charging helps to dissolve sulfation and improve CCA and overall capacity.
The marine guys have tested so called/ marketed pulse desulfating chargers, with no improvements in capacity noted.
The best performance restorative is a combination of the deep discharge/ relatively high amp recharge that gets the battery warm, followed by holding the battery at absorption voltage until either amps stop tapering, taper to a prescribed very low level, or start rising again.
Flooded batteries( and Lifeline AGM) can be equalized. This is an intentional forced overcharge, but ideally it is closely monitored and promptly terminated when specific gravity stops rising, or reaches previously established maximums, or the battery gets too hot, or starts heating rapidly.
EQ voltages on flooded batteries are generally 15.5 to 16.2 volts.
Lifeline's 'conditioning' procedure calls for 8 hours held at 15.5v, applied AFTER the battery has already been held at 14.2 to 14.4v until amps taper to 0.5 amps per 100Ah of capacity.
Odyssey's reconditioning procedure is here:
Lifeline's reconditioning procedure is on page 21, but read everything :
also if this topic is of interest and one wants even more info:
Performing an unneeded equalization/reconditioning procedure, is not just a waste of time and energy, but is likely detrimental to the battery. Such procedures performed on batteries primarily used as starting batteries which are kept at high states of charge/ no deep cycling, are likely of limited/ no benefit.
The TPPL agm needs to occasionally stretch their legs, compared to to a lower $$ AGm or flooded battery. I can baby my 420$ g31 Northstar and beat up My free Dekas, but the Northstar likes a good spanking. If I give the dekas a break, and cycle the grown lazy northstar, that first cycle, it is a petulant. Its voltage falls further and faster than it should, even though it was kept fully charged and floated at the correct voltage.
Take it to 11.9v over 6 hours and feed it 35 to 40 amps until 14.7v is reached( about 35 minutes) and hold 14.7 for about 6 to 7 hours, at which point amps have tapered to 0.4 or less, and the next deep cycle and subsequent cycles it is holding 0.15 to 0.25v more under the same load for the same duration.
I've cycled the snot out of my previous group 27 Northstar. Every time it started to noticeably underperform, the cure was ti intentionally discharge it to 11.9v or less, and then feed it no less than 35 amps until 14.7v was reached, then hold 14.7v until amps taper to 0.4v or less. Only the last 6 months it would not taper this low, and I'd terminate charging once they stopped tapering.
My Group 31 Northstar is not being worked nearly as hard as my previous 27 was, but it still responds extremely favorably after a significant depletion followed by a high amp recharge until amps taper to 0.5 or less. Simple topping up of it is not enough, its got to provide ~50% of its power over 6 to 10 hours, then immediately feed on 40+ amps, when I notice its performance is below that which I expect from it. It will take 40 amps for about 35 minutes before voltage climbs to 14.7v, at chich point amps start tapering. Once they taper to 0.5 or less, It performance is back. Again this is no less than 6.5 hours of charging, and but for that initial 35 minutes, is as fast as it can be charged.
) I have two cars and I don't drive either of them very much. Both have two year old NorthStar AGM batteries. I keep one on a smart Optima 1200 charger 100% of the time. The other I only charge once each week because it sits outside and I don't want somebody stealing my charger. I do not drive enough to keep it fully charged merely from driving it and I don't want to stress the alternator.
