(Is it me, or are battery threads starting to challenge oil threads?)

Not about zink this time, lead! 
I also think batteries need to be excerzised.
Per, you are absolutely right on both counts, here!
I worked with the battery engineers in the 1990s at Gates Energy who created the Optima battery technology (it was for military at the time, went public in 1999). While we can't get those batteries anymore for these bikes (which would be a WONDERFUL thing), the one thing that I learned was most important for any lead-acid battery type is: the lead must be full-density, virgin lead.
The way we "see" this today in batteries is simple: if the same-size battery weighs more (a lot more) from one maker than another, the lead is dense and virgin. As the battery cycles up-down, the lead slowly dissolves into electrons (and some detritus, that white-looking powdery stuff) when the incoming (re)charge can't quite re-create the pure lead that was once part of that cell. The lead breaks down a few lead atoms into electrons each time the battery discharges, and if those electrons, protons and neutrons are still nearby when re-charged, they will recombine. But they are heavy and sink quickly, so some get lost on each discharge cycle. This causes the lead to become porous and contaminated with broken-down acid electrons instead.
The famous Gates Energy Cell from 1980 (we know these as the spiral-wound or "6-pack" battery) has tens of thousands of tiny rectangular holes punched into the lead plates, and then those plates are wound together with thier insulator sheets VERY tightly (6 tons of force) with acid then being captured inside each tiny cell. In those batteries (I have one in my motorhome, now 20+ years old and working fine) the amperage available is almost 80% more than from a normal-sized plate battery, and they are VERY heavy for their size (mine weighs nearly twice the normal-size car battery equivalent). They last for many decades: the ones I had in my portable oscilloscope were just D-sized batteries, but they lasted for almost 40 years. Sadly, when Enersys bought out Gates Energy and moved it to Kansas, they quit making motorcycle batteries that will fit our machines.