I don't understand this. If you can simply charge multiple batteries in parallel with a single charger, then why do they make multi-bank chargers?
Mostly for marine use, where you have an engine start bank, a house bank, maybe a bow/stern thruster bank, and maybe a generator start battery as well.
But most multi-bank chargers do not actually perform a different "charge profile" for each bank. They just use internal diodes to keep the batteries separate so they don't drag each other down, and use one single common charge profile across all the banks. I suspect the Noco GEN series does the same. (EDIT: Though I could be wrong about this. The fact that they specify it as two separate 10a chargers does mean that it just might have two different computer brains - one controlling each 10a charger. Dunno.)
I know that you can, but is it the best way to keep multiple batteries in parallel healthy? Or, say, is any theoretical benefit to individual maintenance just not worth the trouble?
What theoretical benefit would that be? Even if you used completely separate fully programmable chargers for each battery, they would be set the same would they not? Bulk to 14.whatever volts, absorb at 14.whatever volts, float at 13.whatever volts. You have two batteries that are the same, you are going to configure the chargers the same.
And despite Noco's marketing hoopla of "8 stage charging", it is really just a bulk/absorb/float charger that bulks to 14.4v - with a few tricks added. 14.4v is a nice safe number, and that's why this non-programmable charger can be used for flooded, agm, gel, cranking, deep cycle, etc.
(EDIT: For instance, my pair of Chinese 200ah 4D AGMs specify bulk/absorb as 14.6v-14.8v. I have my Victron set to one of its default profiles, which does bulk/absorb at 14.7v, which works just fine. The Noco profile bulking to 14.4v would also work. And with the desulphation and other tricks, like occasionally bumping up the voltage, might actually work better.)
So again, even if it could do a separate and distinct charge profile for each bank (which I doubt) it's simply going to use the same profile x2.
Let's say that two batteries in parallel charge at different rates (for whatever reason). Does the single charger overcharge one to bring up another? Or does it charge one properly and undercharge the other?
Nope. Each battery absorbs at its own rate until eventually, they both reach a state of 100% charge and at some point the charger drops to a float charge.
How would a multiple bank charger "maintain" multiple batteries if they are on the same circuit?
By performing the exact same "maintenance procedure" that it would do if they were on separate circuits. Since they are basically the same lead-acid batteries, the same procedure works for them all.
Up until now I was using the 2-back charger to maintain both the engine and coach battery and they are very different batteries. It's worked well and I was disconnecting them manually during mainte[nance.
It worked well not because you were separating the batteries, but because the Noco's maintenance procedure works well on all lead-acid batteries.
Thanks, definitely making my brain work today.
Cheers, that's one of my favorite pastimes.