I used to have several bettas, however they all died with old age(well, i accidently left one in the car while moving in the middle of winter and he froze because i fell asleep

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I've kept them in several tanks, though nothing smaller than two gallons. In the wild they live in huge rice fields where although the water is shallow(as low as 2'' in some areas) it can be thousands of gallons in total because they are so widespread. They can also be found in smaller puddles as you mentioned, however not much smaller than the size of your average rug and three or so inches deep.
Cheers,
Art