Anyone build general battery packs?

[The Mad Atheist]

Planning on getting this, https://motohorn.com/liquidation-sale/ , for my bicycle and will need a pack that'll supply 12v 20amps in a water bottle sized package that'll fit in a water bottle cage.
Think a 3S of either 18650s or maybe 21700.

 

[cpufrost]

Go with 21700s for sure.

 

[The Mad Atheist]

Go with 21700s for sure.

I waited too long to snag one for the low price and might instead get the Loud Classic, https://loudbicycle.com/horn#classic .
Not a fan of the new one that dangles in the wind, waiting for some punk to rip it off. Tho I'm curious of the droid horn now since I just saw the update.