Btw, I use keeppower IMR 18350’s 1200mAh cells, depending on where you’re from these may or may not be available and/or cheap. They also come in a protected variant which might be more suitable for you.
@Jennison, you are not a dope.
You just need to learn a bit more.
For staters, I would just get a Samsung 30Q from any of these US websites:
It is a balanced 3000mAh 15A(underrated) cell, so should do well in about any light.
They are looking for an 18350, not 18650. And @Jennison you aren’t a dope! You’ve made a good decision by joining this forum. You’ll learn a lot. Take some time to learn about li-ion batteries. They can be dangerous if not taken care of properly.
“The only stoopit question is the one that’s not asked.” We were all n00bz once, don’t fret it.
If you open the light where the cell goes and see a spring or nipple on the LED end, you can use flattops (recommended over button-tops). If only a flat area/pad, then you’ll need button-tops.
If the light itself has LVP (low-voltage protection), then you can use an unprotected cell (recommended). If the light doesn’t have it (blinking when voltage is low doesn’t count; it has to shut itself off), then you should use a protected cell.
I don’t have an S1, so can’t speak to what it has or doesn’t have, so someone else can chime in.
We’re a friendly bunch. You can shave your head, pick up your goat-leggings, and sign over your bank accounts later. No rush.
The Astrolux S1 appears to be a BLF A6 with just the 18350 tube.
Young Man!
I’d like to speak to your Manager.
I was PROMISED goat-leggings
Three Weeks Ago, and they’re
still not here……
. . —————— Karen.
The S1 is a solid choice. If you count the BLF A6 version, I have three. One thing I did though - I found 18650 tubes for them (not very expensive) so I could use the more common and higher powered 18650 batteries instead of the smaller 18350. Then again, the smaller size might be what attracted you to the light in the first place.
Where are you located? That can have some impact on the best place to buy batteries and accessories.
FYI - there’s this weird little forum that has lots of cool stuff about lights. They even have a quite nice review on the S1 . Please excuse the fuzzy images. Photobucket iz da debbil.
Note - there are often variants of any given light over time. Keep alert for hints about what version of something you’re reading about - particularly if the entry is old.
I’m in the Boston area, but it also seems there are options on places like eBay, unless that’s not a good idea. So now I know I need a size 18350 and can use a button top (there are springs on both ends of the interior). What’s left:
I can’t tell whether I should use a protected vs unprotected cell (doesn’t come with any instructions) or what mAh is optimal and available for this light. Lastly, are all of these cells rechargeable? I want to get a cradle too for whatever battery I do get.
I want to thank everyone who has kindly chimed in thus far. You guys are an extremely helpful and friendly bunch. I wasn’t sure anyone was even going to bother to respond at first as all the discussions are so far beyond my question. Boy, am I pleasantly surprised.
Jennison
Unless you know about batteries & and their sellers, avoid Ebay for that. Since you are in Bean town, try Liion Wholesale, as they are in Pennsylvania. If you order in pairs or 4 packs, they ship them in cases (cradle) automatically. They sell authentic batteries, and test each batch they receive for labelled specs. I buy vape and flashlight batteries from them.
Whoops, misinterpreted cradle for a charger. I would get one that has a digital display, that shows voltage and mah it’s charged so far. I use a Xtar VC2S at work, and a MiBoxer C4+ at home.
I’d recommend against eBay for batteries. There are a number of reputable sellers in the US that can help you. Off the top of my head,:
https://mahbattery.com/
and more that are not coming to the top of my mind.
If you have springs top and bottom, I’d go for a flat top.
And yes. these batteries are typically ALL rechargeable. The sites above will have good charger options too. Just make sure the charger you select handles the short 18350 cells.
Side Note - be sure you’re looking at li-ion, not lifepo4 or anything else.
Thank you, all extremely helpful. I hope not to become a lightaholic because of you guys!
Jennison
Edited my last post, added a line at bottom.
Well, this is why it is recommended that folks with drinking issues not hang out at the bar… 
Unless I’m not interpreting the info correctly, seems like a lot of these chargers can be adjusted to accommodate different size batteries. Is that the case?
jepp usually they take all kinds of batteries.
I find that kind of hope in the recently infected rather amusing. 
If you fail to become a flashaholic, that means we failed.
We don’t fail.
Can you send pictures? I can give 50 points to your account. Can you check post office make sure?
Uhhh, yeah, good luck with that…
Young Man.
My neighbor got hers,
but mine are still missing,
forcing me to go legging-less.
I Demand Recompense!
. . —————— Karen.
Can you send video? Please go post office check. I can give 50 75 points. Happy?
Young Man!
I Never Agreed for my
Goat Leggings to be outsourced
to BangGood!
I DEMAND a Second Pair,
a Complete Refund, and
the firing of someone!
. . —————— Karen.
I understand. Can you send video? Please check local post office.