Need a little help!

I sent for an Olight S20 flashlight & am waiting for it to arrive. The design of the S10 I have already is pretty good and I don't pocket carry, so the issue with the switch isn't a problem for me. The tail-mounted magnet is pretty handy. I have CR123 batteries already, but am looking into 18650's as well as an option for longer battery life, cost, etc.

The problem I have is with the size of these batteries. The more I read about the 18650, the more confused I get. While I know they are much better in energy density, the number of differing lengths, manufacturers and capacities is turning into a nightmare as far as one which will just fit and run. It looks like there are too many choices in length for me to decide on the correct one. Is there enough internal capacity in the flashlight's body to take any cell, or should I be more careful in buying one that will fit properly? I don't want to "over think" this, but it costs money to make bad choices and I don't want a selection of cells which don't fit.

I would like to try the Panasonic 3400 protected battery, because it looks like a great deal for the available power, safety & all around good quality, but if it doesn't fit, it's a waste of time & money. Thanks for your input.

I don't think you will have a problem at all. I think the issues early on were lights designed around 2x cr123 batteries. I have 4 different size of 18650's and a couple of years ago there were some lights that were tight or poked out too far. Nowadays, recently manufactured lights that specifically state they take a 18650 means you should be OK.

There are some lights that say they won't work with flat top cells and have to have a button top. They do that to protect the circuit in case the battery is inserted backwards, but the S20 has a spring up front so a button top or a flat top should be fine which means that the length shouldn't be an issue either. If you want a battery that might be more versatile to other lights, I'd probably get a button top. To me it looks like the S20 is made more for 18650 with the option to run 2x CR123 by utilizing the sleeve so that they don't rattle.

I don't have the S20 but I would give it a try. The only reason I would own a light like this is that it will do 18650's. So if this was me and the S20 didn't work with 18650, then I'd be selling it before I'd sell the 18650 battery...........specifically if the 18650 was a well known battery.

My guess is that the S20 will take any 18650 battery that you can buy. You already mentioned that you are after a Panasonic 3400mAh battery (good choice) and so there are a number of protected 18650 batteries that utilize the Panasonic cell.