Something I should have added is all the batteries I’ve listed are UNPROTECTED, so you will need to be aware of the safety risks of using an unprotected battery, lots of info on that here if you search the forum, but mainly be sure you don’t run them down too far during use. Also use a quality charger so you don’t risk overcharging them. Best to use a DMM/voltmeter to check their voltage often and keep them topped off. I try to not let mine get below 3.5v, and NEVER below 3v. Also it’s very important to be careful not to leave the flashlight turned on by accident.
Of course there is much more to be said about Li-Ion battery safety, protected or unprotected. Use the search words “battery safety” here on BLF and you will find a ton of information. Here’s a good resource thread: Lithium-ion battery safety 101
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You could use a protected battery in the S1/A6 but again you won’t achieve maximum output on turbo. The protection circuit limits the amperage draw to around maybe 5-6 amps max. None of the really high drain battery’s are fitted with a protection circuit because it would defeat the purpose.
As far as the 20A rating on Banggood in the title they are probably referring to pulse not continuous, I’ve read pulse is typically considered to be around 30 seconds, if you look in the description in Banggood under “specifications” you will see the 15A spec: “Max. continuous discharge: 15A”
On my A6 I really can’t see much difference in brightness between a 30Q and a 18650GA, maybe if I had two of them I could notice a difference side by side, but I think the main reason is the springs are not bypassed on mine, so the GA possibly supplies enough amperage for mine.