wrcsixeight,
I read your post several times, as I'm not as well versed on batteries as you are, and wanted to be sure I understood what you're saying. Exactly what are you referring to when you talk about all this, "deep cycling"?
bringing a battery from 90%+ charged to 50% charged or less, then recharging back to 90%+ charged is a deep cycle.
Actually it is a partial state of charge cycle.
Cycling a battery is much harder on a battery than always sitting at high states of charge, and the deeper the battery is discharged the more important, to its longevity, it becomes, to return it to high states of charge, and ideally, 100% state of charge.
The battery becomes more and more difficult ( taking longer) to return to ideal 100% state of charge, as it ages, and aging is accelerated by not being returned to 100% state of charge, but more so when it is deeply cycled. Heat is destructive to batteries, as is overdischarging, but if these two are not factors, then cycling the battery is the next most effective way to reduce its lifespan, but especially when it is not returned to 100%. 98% charged is far far better than 92%, but half as good as returning it to 100%. in terms of ideal/ maximizing longevity.
So a battery which lives underhood for 6 years only as a starting battery is living a respectable lifespan, but if it were living underhood and deeply cycled 500+ times, that would be impressive. Shallow cycles are not nearly as detrimental, and simple engine starting uses a tiny fraction of the battery capacity.
Short trip driving is not destructive to the battery itself, with modern fuel injection and easy starting engines, but short trip driving never has the time required to bring a 80% charged battery to 100%, which is never less than 3 hours. I measured it taking about 45 seconds for my vehicles charging system to return the energy to the battery used to start the engine. But 45 seconds has no chance to take a 80% charged battery above 80.1 % charged.
Any charging source applied to a less than fully charged battery is a good thing, as long as it does not overcharge.
AGM is a Lead Acid battery too, its electrolyte is just absorbed within the glass matting and not free to slosh around.
One should really refer to 'regular' lead acid batteries as 'wet' or 'flooded'. People also like to refer to any sealed battery as a 'gel cell.' This too is inaccurate, and misleading, as while there are lead acid batteries with gelled electrolyte, actual gelled electrolyte batteries are rare, as if they are charged too quickly, voids will form in the gel, destroying its capacity as there is less surface area for the chemical reaction to occur.
Actual gelled electrolyte batteries make excellent deep cycle batteries, when their recharging is kept within its limits. They are not good candidates for automotive applications.
A charging source is basically seeing to bring a battery upto absorption voltages.
a 1 amp/ 1000ma charger has this much amperage available, to bring the battery to absorption voltage.
A well discharged battery will accept 1 amps for quite a while before voltage rises to 14.xv
A battery at high states of charge will not require very much time for 1 amp to bring it to 14.7 volts.
When absorption voltage is reached, less and less amperage is required to maintain the battery at absorption voltage, and when this amperage tapers to very low levels, or stops tapering, then the battery is fully charged or very nearly so.
So all smart charging devices have a certain amount of amperage available to achieve a maximum voltage, and once reached, it limits the amperage, if it did not limit amperage voltage would keep rising, and there is little point in bringing a battery above 14.8v as it is not going to charge significantly faster, but it will offgass much more and heat up much more and degrade the plates faster.
Different Chargers will hold this absorption voltage for different amounts of time, but most have a one size fits all approach, or a 3 sizes to fit all approach, with extra special marketing to make the consumer believe it can defy the laws of physics.
Most are more than good enough, for a shallowly cycled automotive starting battery, but most will fall far short of ideal or even acceptable, if applied to a battery that is regularly deeply cycled.
When Lead acid batteries are discharged farther, especially below 80% state of charge, it becomes more important return them to high states of charge, relatively quickly. When they live chronically undercharged, getting them back to true 100% charged becomes more time intensive, requiring longer times held at absorption voltages. Getting a regular smart charger to hold these higher voltages for as long as is required to achieve this, can be a lesson in futility.
If one were to use a hydrometer on a battery with removable caps, they would see that most smart chargers stop charging when specific gravity is still well below the 1.275 'green' area.
But almost nobody ever does this, instead believng the marketing and the green light on their charger, and for most, it is not important as the battery will easily start the engine, and for most 'going strong'
But if that battery is regularly cycled deeply, intentionally, achieving maximum specific gravity of all cells, the true full charge, becomes very important to get an acceptable lifespan from the battery.
When the automotive starting battery is slowly drained to 30% state of charge over 3 weeks from parasitic draws on an undriven vehicle, this is also a deep cycle.
Jumpstarting and driving for an hour, at best, will get the battery to 80% charged and 80% to 100% is no less than 3 more hours, and likely far longer than this. Idling parked to recharge a battery requiring a jumpstart, can overheat an alternator as it will be fully fielded, outputtng all it can into the depleted battery.
Do note it is still possible for a 30% charged battery to easily start a modern fuel injected engine, in mild climates, when it is still healthy, but it will not remain healthy for long if it is often slowly drained to 30%, often, and never recharged to truly full.
My Dad's Noco Genius 1 that I tested on the AGm setting, once it got the battery to 14.7v, stopped outputting amperage all together, and only restarted once the battery voltage declined to 12.69v.
Some other maintainers will have 500 or 750 ma available to hold the battery at a float voltage. Some of these might first allow those max potential currents to achieve absorption voltages before then dropping to float voltages. Some really cheap ones will not and will only seek float voltages with their 500 or 750 ma rating.
Ideal float voltage is dependent on the specific battery and its temperature, and generally AGMS will say to float at 13.4 to 13.6 while flooded will be 13.1 to 13.3 at 77F.
The Noco genius 1 does not try to maintain the battery at any given voltage, it will, after bringing the battery to absorption voltage, shut off, and restart once battery voltage has fallen to 12.69v or so.
Knowing battery voltage is better than not, but knowing how much amperage the battery is accepting at that voltage( electrical pressure) is quite revealing, just like knowing how much voltage the battery is able to maintain, when starting the engine( load test).
For example a battery maintaining 12.7v charging a smart phone at perhaps 10 watts max load, reveals little to nothing, but o a battery which can maintain 12.1v providing 1800 watts, is impressive.
When charging ,measuring 14.4v is good, compared to not knowing the voltage, but is the battery accepting the 5 amps at 14.4v, or 0.5 amps.? 5 amps might reveal the 5 amp charger is still maxed out, trying to achieve 14.7v with all its available amperage, or that the 10 amp charger is only needing to provide 5 amps to maintain 14.4v. The 5 amp charger would still be in constant current mode, the 10 amp charger would be in constant voltage mode.
The amperage a battery accepts at a measured electrical pressure( voltage) is extremely revealing, but that electrical pressure alone, is not.
