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