Absorption Stage starts when amps begin to taper from the current limit amps of the charger.
The SOC of the battery when that happens depends on the charging rate-- the amps of the charger (its max current limit) wrt the size of the battery bank in AH. Higher charging rate, lower SOC when tapering starts. It can be 65% or 95%, whatever---and that's with Wets!
At about 20% charging rate (20 amps on 100AH batt) it was 87.5% SOC when amps started to taper at 14.4ish volts with my SiO2. Battery voltage got to the charger's 14.6 volts by the time the battery was fully charged.
Since an ordinary AGM would have started to taper at more like 77% at that rate, that means at 20% rate they charge at the same "speed" (and so generator time) until about 80% and then the SiO2 is "faster" after that because it is still accepting the 20 amps while the AGM's amps are tapering. But you don't charge them to full with a gen anyway--usually to 80 or 90% to not waste gen time when camping. In that case the 80-90% of SOC would have taken less gen time. Whether that many minutes of gen time matters "depends" on the situation at each the RVer is doing a recharge. Some days it won't matter at all, others it might.
Guys who have them report Lis will not taper until in the high 90s SOC (and that is with lower charging rates) , but also since both SiO2 and Li do not need to be fully recharged every cycle to prevent suphation, and if you do stop the gen at about 90% SOC using a 20% charging rate, they would be the same "speed" in practice. The claim they go to 97% before tapering is at a lower sort of charging rate. Heck, you can charge Wets at 5% rate and not see tapering until 95% or whatever. solar is like that with its usually low amps making for a low charging rate.
You could use a much higher charging rate with Li but you still need the charger to do those high amps and a gen that can run that much of a charger. There was a graph for LFP that showed amps started to taper at lower SOCs with very high charging rates like they can take, so it is the same with them. Just with higher rates.
"Faster" charging has to be defined exactly or it amounts to bogus advertising. A 55 amp converter will not charge any type of battery at more than about 55 amps! :(
If you start the recharge at 20% SOC like you can with Li or SiO2, you get a longer Bulk stage than you can with Wets and AGMs starting at 50%.
So that is another way to be "faster". More SOC range= more AH=at the max amps of the charger. More gen time to do a 20-80 than a 50-80 of course, so it takes longer to be faster that way :)
Your battery "sales rep" will gladly tell you how much faster it all is! ("BS baffles brains"-is something in Latin for such sales talk)
