I'm goofing around with my blackbird battery which I think is fine, but has a 8.8 VDC [too low] cranking voltage. Bought in 2019 [four / five years old, mild climate] realized eventually that my new charger failed to apply charging voltage if the initial battery voltage is 12.6 or greater.
So I don't get it until I'm putting my new smart charger across three different batteries and nothing's happening.
Then I put my 30 [forty year?] old charger across two jumpered in parallel and monitored the applied voltage - 15.0 to 15.1 there is a 2A / 6A rocker switch [which has been stuck in 6A mode since I wore platform shoes... that's an exageration; I never wore platform shoes].
Now, I wouldn't try this at home, I wouldn't [given the delicate electrical "stuff" of the BB much less the ST] put this on against the connected electrical circuits of either bikes, but disconnected, they sure sucked the juice [nothing like an analogue ameter, to tell you where it's at], and afterward my BB battery [for the first time held a 13.0 static VDC and started a lot crisper. Will compare the actual improvement in cranking voltage [or voltage drop, however you like to look at it] tomorrow.
I'm advised on the BB site that the charging system is a net looser; I know this to be not so with the ST; lower than ideal initial battery voltage [albeit with a good battery] that has been sitting for a couple weeks you can feel the slower crankspeed but after a short ride with everything [that came with the bike] it always recharges that battery within thirty minutes.
The ST is a 240 CCA whereas the BB is a 210CCA. My opinion is that the 210 is garbage and root cause of various electrical problems with that bike, but story for another day.