each cell 3,2V 1,1AH

to get 48v you need 15 cell's in serie 15 x 3,2v = 48v

to get 20AH you need 18 cell's in parallel 18 x 1,1AH = 19,8AH

total cell's 15 x 18 = 270

put 15 cell's in serie then take 18 pack's ( of 15 cell's in serie) and put them in parallel.

(-)-----48 v ----- (+)

-1-2- ..... -15- 1

-1-2- ..... -15- 2

.

.

-1-2- ..... -15- 18