Thx for the great info. I guess I will shop online for some Panasonic 3400, maybe I can find a kit that comes with a more reputable charger as well (bc I'm not going to be standing around waiting for batteries to charge).

What is "protected"? And what characteristic does mAh measure? Is that supposed to indicate runtime, or power, or ...? (It's been a long time since undergrad physics EM theory...) When you say "often don't break the 4-digit barrier", do you mean it may actually be < 1000 mAh?

I did actually recently buy a (cheap) multimeter, this will be a good opportunity to play around with it! My current charger does have an indicator that goes from red to green, which I assume means it stops charging. I should test them right when they go green, and then another time leave them in overnight and test to see if they overcharge.

As for heat, hopefully I can ride fast enough to keep sufficient airflow! But I don't know about heat-sinking. I don't see any obvious fins or blades or anything like that. The lens is quite thick glass, that seems robust, and the LED is maybe 4-5cm behind the glass, I don't know if an air chamber that size can act as a heatsink or not. Would it be recommended to drill pinholes in the side of that chamber?