Mouse Milk BFL
"Sterling" is as British as "Chatham" or "Fartface At Sea"
I have far too much experience with true A.C. Eddy Currents circulating in alternator stator laminations, perhaps 3x10 as powerful as what a string of batteries can produce. Precision indexing of rotor halves, and uniform coating of silicon on stator laminations can reduce heat as much as 22c Delta T.
But at the scale you describe it is almost a mockery of professional electrical engineering. A 7th Grade Science Project.
A pair of DC/DC boosters with precision voltage regulation and a voltage comparator (meaning an interface) would ensure priority balanced charging. This would be useful if a second bank was remote as with a trailer and a main connector line that could deliver full charging potential when called upon to do so. This simply isn't your Gizmo.
I would not use a Gizmo even as a gift. There are a hundred ways it can fail and a majority of them can damage the batteries. Risk the potential cost of Lithium batteries? I don't think so.
