Alas you support what I have been saying all along...
Any load change causes a voltage drop or increase that the alternator response to. Modern alternators can respond fast enough to make headlight dimming unnoticeable, but even old alternators usually respond well with one second.
Yes - 14.4V (2.4V/cell) is the highest charging voltage for lead acid batteries (wet or SLA sealed). Above that, noticeable gassing starts etc. Above 14.4V is used for battery maintenance - eg equalisation & recovery.
The voltage required to "fully charge a battery" is 13.8V - ie, 2.3V/cell. (But that is insufficient to remove (soft) sulfites.)
A fully charged battery takes its float current, not 0A (zero Amps). Float currents are typically 100mA - 2A for automotive batteries,.
Though a (cheap?) battery charger may "stop" charging batteries, an alternator does not.
Whilst an alternator is operating, it is charging the main battery (etc). Vehicles do not disconnect the alternator from the battery when the battery is full.
Whether batteries maintain charge or whether one discharges into another parallel battery is independent of their internal resistance. That latter is solely dependent on whether the battery's "internal voltages" match (ie, their OC terminal voltage at any given time).
Be aware that the above merely adds to your info - it does/should not contradict it.
I knew what you meant by "fully charged" (whether 14.4V or 12.7V) but some would read your first reply as saying that a fully charged 12V lead-acid battery is 14.4V. (Whereas it should be 12.67V at STP - ie, 25C.)
AFAIAConcerned, in no way do you disagree what I have been saying for years.
As to your last paragraph, that's what the UIBI/charge-light controlled and voltage controlled isolator do - they only interconnect batteries when charging - hence no "high discharge currents" from battery(s) to other battery(s).
However diode isolators are a different and independent issue. But see Simbalage22's problem and other Simbalage discussions for ramblings about that.
But I see no need to continue this side debate unless there is a supporter for Red.
Should Red or anyone else wish to continue this paralleling discussion, then start a NEW thread specifically for that purpose.
This constant hijacking of threads is pathetic.