flashlight

I've generally heard that it's ok to discharge LFP batteries to 0%. You just shouldn't store them that way (or at 100%) for long periods. Keep in mind that LFP has maybe half the energy density of the highest density NMC batteries, and sodium has maybe half that of LFP. Sodium really doesn't sound that good batteries for portable devices.

I'm kind of liking the form factor.

Having grown up with mag lite being the new consumer thing that actually worked, there's something to having a beefy light in your hand.

Sodium batteries are mostly of interest for grid storage or maybe stationary home batteries once they get cheap enough. They are sort of marginal for EV's but might find a place in some cold weather ones. Having them in a few weird flashlights isn't going to help ramp up manufacturing volume compared to that. The real demand will come from power utilities buying gigawatts at a time, not a few flashlight nerds.

I remember the Eternalight and it went through a few nicer incarnations over time The designer was a regular on Candlepower Forums. IDK if the company still exists. The product was cool in some ways. IIRC it uses 5mm leds. The first production flashlight with a Luxeon was the Arc LS and I had two of them. I think the semi-custom McLux TK may have been earlier but my memory by now is hazy. I still have mine. Sodium batteries are different. Aside from the very niche advantage in cold weather charging, they are worse in every way than lithium. The main feature that makes them interesting is potentially lower cost per KWH in the long run. That's great if you want a 100KWH off-grid battery for home, and maybe it can find its way into economy EV's. But nerdy flashlights, nah, battery costs are not much of an issue already. The bigger light and fancier charging and regulation circuitry negate any advantage. We could already use LFP batteries if we wanted to, but we almost never do.

It wouldn't surprise me if there's not yet any sodium charging chip for small consumer electronics like this. I haven't heard of a sodium powered flashlght, phone, or anything like that before. The only sodium consumer device I know of right now is a Bluetti power station which has 900WH: https://www.bluettipower.com/products/sodium-ion-battery-pioneer-na

It got some attention at its anouncement but tbh it's 10lb heavier and $300 more expensive than the 1024WH lithium version (Elite 100v2). So it's for early adopters only.

If you want to charge a small sodium cell, you can probably program an MCU to deliver the right charge profile, along with a few small external parts. That's how Apple phones worked at least in the past. They saved a fraction of a penny by just incorporating some extra logic and code in their big ASIC instead of having a separate charging chip. It's kind of interesting that the charger was programmed in Forth, on a special Forth processor (b16-small) that they cooked into a hardware macro: https://bernd-paysan.de/b16.html . They hired Bernd (the b16 designer) to write the code and it was pretty intricate because of the cpu's limitations. I don't think I'd have used that approach ;).