or to put it another way:
It seems that everything is working fine and the problem is likely? a high drain element that is taking more than the generator can supply, leading to flat batteries.

Have you tried going for a run with a good battery and NOT using the headlight?

I personally am a bit of a fan of those Shorai batteries as they are very light weight.
However, it seems that the Amp-Hour rating stated for them is fairly optimistic.
In reality, closer to half of what is stated I suspect.
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...