In the good old days we had flooded wet cell lead acid batteries and they all pretty much took a charge about the same. But technology now has different battery makers building batteries - wet cell, absorbed glass mat, gel cell - differently. And I actually believe that when a battery maker specifies a specific type of three-step or four-step charging curve as being optimal they know what they are saying.
Without verifying the numbers I suspect that most any 12 v charger can charge most any 12 v battery to somewhere between 80% and 90% (or maybe a little higher) of full charge. The penalty the owner pays for using less than the optimal charger for a specific battery is probably less than full charging and maybe reduced battery life.
What I pay the most attention to is the peak charging rate allowed - because charging a battery too slowly or to less than 100% does not kill a battery, but charging at too high a voltage, or at too high a current rate can overheat a battery, warp plates, cause internal shorting, and other ills. They are packing things a lot tighter in the cases now compared to hanging some flat lead plates in an acid bath.
I am not sure there are any good general rules because even batteries of the same type - AGM for example - differ in construction, internal clearances, etc.
The best thing to do is to see what the battery maker has to say, and to avoid charging at a higher voltage or current than they recommend. That might mean buying and owning a special charger. Or it might not. Less is more - more is not.
If you are the eternal cynic and believe that folks who make their livings building and selling batteries really just want to rip you off selling a battery charger they don't even make, well you could be right but I doubt it. It seems to me battery makers survive and thrive on the reputation of their batteries - not some Chinese battery charger. So when they advise a specific charging curve as supplied by a specific charger, I tend to believe them. We went 10 full rounds on this with BMW and Deltran, until Deltran finally agreed with BMW's and Exide's position about a special charging curve for their gel (not AGM) batteries.
As one that previously posted on the Forum about having bought a Die Hard float charger, now it seems timely to get this out there. I put that float charger on my T@B trailer RV to maintain the two series 27 deep cell , conventional wet acid batteries. It proceeded to boil them over rather than its intended duty. Rather than risk further damage I took back the charger and just need to warn against others depending on that charger for their bike battery.I was thinking of Die Hard as a brand name charger to be depended upon but evidently not!
I have been using a Battery Tender around ten years old(not the Plus model) to maintain my bikes battery in the winter , to include my Westco thats ~ 5 years old now.
I once tried the Wally World cheapo? float charger on my bass boat deep cycle battery and it was overcharging the battery .