There was another Equinox battery thread where I posted the following:
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Right, no memory. And the Nox should shut down before the battery gets so low that the battery might get damaged, just like a cellphone. In fact, I'd say treat it like a cellphone. No benefit to "full" discharge, no harm either.
They say these type batteries can be recharged 300-500 times, but that's only to "significant loss" of capacity, 50% maybe? It's not like it just up and dies. Lots of little charges are slightly beneficial over fewer full charges. Keeping charge level between 20% and 90% is slightly beneficial. Tesla cars use similar batteries, and their owners have figured all this out because they don't want to fork out thousands for a new battery. For a Nox, it's not gonna hurt that much. Charge it however works best for you.
Keeping it on the charger vs taking it off when full...depends a lot on the charging circuit. It's probably fine to leave it on there, but since these batteries self-drain so slowly, I take it off. No big deal if I leave it on there a week instead of a day, it'll be fine. I wonder what the manual says...
From the manual:
Battery Maintenance -- Lithium-ion battery performance may degrade if unused for long periods of time. Fully charge the battery at least once every 3–4 months to prevent this from occurring.
It doesn't specifically say but this implies to me DON'T leave it on the charger forever.
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You are correct in your findings about optimal charge percents, but I doubt it's going to gain you very much. It is interesting that the charging is different from a power bank rather than a USB port, I have no explanation for that. In any case, I prefer to let the machine work for me, rather than jump through hoops working for the machine, but to each his own.
I have a USB port voltage/current monitor, which I put on my Equinox charger. The machine was fully charged a couple weeks ago, so should be close to full still. It started at ~350mA (the USB charger is capable of 2A) and I watched it slowly decrease over a few minutes. I don't know how long it took to get to full, but when I came back several hours later it was done, solid green, and pulling 30mA. I would not leave it like that indefinitely, but for a few hours or a day even, not a big deal in my opinion.