I have a 18650 light that’s won’t be used very much regularly, mostly for emergencies where I need a bright light. How often should the 18650 be recharged? I’m new to 18650 flashlights and don’t have a feel for the self-discharge rate. It’s a Convoy S2+.
If you have the new 12 mode firmware on your S2+, it has battery check. I think it is the last mode, 4 out of 4 blinks is a full battery.
I don’t think S2+ has any self discharge concerns, unless you do some cool mods like glowing tail switch…
Then of course depends on the type and age of your batteries and if you subject them to extreme temperatures outdoors ….
I have some very old Sanyos, they need to be topped off 1-2 times a year,
I don’t bother charging new Samsung 30Qs, I keep them indoors, so they don’t get too cold or overheat, maybe after 2-3 years they might need to top off.
That’s surprising. I guess I’m used to laptop computers, which probably have some parasitic drain even when in the off state, so my gut feel for 18650 cell self-discharge over time is probably higher than they really are.
Thanks
Better than just “topping off” every so often would be to just get an identical light, and rotate ’em. Use A and store B, then when A needs a charge, charge it and use B but then store A, and so on.
Just topping off a Li cell without using it would be like keeping a balloon filled to just about busting and leaving it until it leaks a little and then stuffing it again.
li ion cell discharge rate is about 1% capacity per month
so 100 months from 100% to 0
i;d do it more often but a year or two should be fine
wle
I know I’m not supposed to… but I keep 18650 zoomies in the car dash. I pull them out twice a year and charge them up. I’d say they do very well holding a charge as they typically hold over 4V when I check them before charging (and I often only charge to 4.10V for those batteries too).
I DO use REAL Panny Bs in them though… no “knocky-offy” batteries in the cars. I use the fake 18650s in my solar pathway lights I have all around the house and garage (and rebuild about once a year too)— but only IF they can hold some juice.
The really cheap crap 18650s (like you sometimes get with an el’ cheapo AliExpress $3 light) usually go right into the recycle pile. I’ll test them for fun sometimes… but I usually am wasting my time when I do. 
I’d go with, twice a year, take the cell and discharge it (as low as 20% if you like) and then recharge, then toss it back in.
Just thinking… (Oh, so that’s the burning smell.)
What about getting a SP32 or similar light that can handle a 2S arrangement, at least a pair of ’123s, and, well, use a pair of ’123s inside?
Those beasties have something like a 20yr shelf-life, and you’d only be hitting the driver with 6V, not even 8.4V, and use the S2+ around the house or something?
My MH20 can handle ’em, and I was burning down a few “free” ’123s that came with hotwire lights.
They’re pretty much unaffected by heat or cold, tried’n’true (PD/FD/mil), so… why not?
That makes sense. I have other 18650 light, so instead of buying identical lights, I might change out the batteries. The emergency part I was thinking of is actually to maximize turbo mode in case I need it.
Had an incident recently that made me realize how disorientating it is to have a bright light in your face. And as much as I don’t like confrontation and don’t feel safe owning a gun, a super bright flashlight is a pretty good thing to have handy. I’d like to keep it above 3.9V to maximize the Turbo mode rather than let it run down to 3.0V before changing out.
You may do well to look into “tactical” lights (not to be confused with the common “tacticool” lights). Main features: Can take primary cells (to be stored for emergency use, and quick-swapping instead of waiting to charge), and direct access to strobe/turbo (ideally both). Also frequently forward-switch and weapon mountable, but that’s not an issue here.