Voltage tells part of the story.
how many amps are flowing at that voltage tell nearly all of it, especially with repeated observations of both on the same battery as it charges, or discharges.
All chargers should be equipped with a digital ammeter, and a voltmeter in my opinion
Anybody wanting to know what their charge ing source is doing should put one of these, or similar, inline on the DC output.
it will show volts, amps, wattage, Amp hours, watt hours, Peak amperage, peak wattage, and minimum voltage. Some of them show also will show the time they have been connected, and passing current though this clock has been inaccurate on some of the versions i have employed, making the watt/hour reading inaccurate.
Those who prefer ignorance should not bother, but they should also not be recommending others employ the same strategy.
Those not preferring ignorance or blindly believing the marketing literature, can see how much current the battery is accepting at the voltage the charger is seeking, or allowing, at higher states of charge.
the amp hours delivered, can tell them how discharged their battery was when they put the charger on it. the more observations the better idea one can get about the behavior and health of their battery, unless they prefer ignorance and to believe marketing literature/ deceit and experience free internet experts.
If one sees that their charger is going from 14.5v absorption, to 13.2v green light 'float', while still accepting 2+ amps, they can see their charger is not fully charging the battery.
Once one intentionally cycles and observes a battery, through proper measurement tools, from spanking new, as its health declines, it becomes obvious that so called 'smart' chargers, are just compromises that feed on ignorance of the consumer and the BS repeated Ad naseum online by those with no experience actually doing so.
But any charging of an underdepleted battery is better than no charging, and 'Ideal' can be taken to unrequired extremes, especially for a starting battery on a modern fuel injected vehicle that needs only a tiny fraction of its rated CCA to perform the desired task of starting an engine. One would be surprised at just how small of a sulfated battery can still perform this task. The benchmark of achieving 'still going strong' apparently means the battery can still start the engine, which is no difficult task with modern fuel injected engines.
a 400$ TPPL agm, deeply cycled, intentionally or not, with a small amperage charger as its main charging source, is going to live no longer than a 89$ flooded battery.