just bought a sofirn if25a and comes with a 21700 batt. but doesnt say if its a
button top or flat top battery.3-4 weeks from china and want to buy a spare
b4 it gets here.anyone know if its a button or flat top 21700? Thanks…
new to blf first timer.
Either works fine.
I grabbed my Molicel P42a (with a REAL current capacity of 30 amps- tested by Mooch) and the light gets HOT FAST with that battery! After several trips out on some warmer Kansas nights, I finally tried a 50G instead. Got very close to the same output (I use turbo for a few seconds tops)- so to my eye about the same output but more capacity and… LESS heat up front. 
After burning my hand some, I prefer a higher capacity 21700 like the 50G (10A continuous at 5kmAh’s). But soon I’ll be using Molicel’s latest 21700: the M50a (15A continuous also 5kmAh’s- this should be like the 30Q of 18650s with a nice mix of capacity and current output).
Check out 18650Batterystore’s deal of the day (right now) if you just want one or two great batteries. The Epoch 21700 5000mAh 10A Battery (a re-wrapped 50G) is going for $5 each. They are based in Atlanta, GA. They ship fast, sell authentic batteries (no fakes) and they charge FAIR pricing for shipping too
And WELCOME to your new habit! 
The batteries with recessed heads might not work. At least, my 21700 tesla (the one with 3 straigth indentations at the negative terminal) doesn’t work.
Huh…
I’ve used several (different) flat top 21700s- no problemo!
But the OP’er can order “button tops” in the Epoch 21700 sold at 18650batterystore.com (again… a re-wrapped 50G) for the same deal right now- if he’s not looking for a “hand heater” light 