I am looking for the Battery connection and how many there should be in the unit. the Model number is an Prestige EXT 1250PS2E

The 2000EXT (and I think all other smaller Prestige units) run 60 volt battery strings, so the internal cell loading is 5 cells. With the unit's plugs facing you, three on the left - terminals to the outside, and two on the right nearest you (vacant behind the fan), terminals toward the board. small jumpers between the two pairs on the left, and the pair on the right, red to black. Jumper the two at the fan end with the long jumper, and then red to red and black to black on the leads from the board onto the two open terminals on the two cells at the rear of the unit, and be aware, there will be a small spark on connection. The connector on the rear is for external batteries, which are not required, but if you have the cabinet, you can use those as well, although on mine, paralleling batteries (as per the Prestige design) has resulted in some ugly battery failures, when on strings faults a cell, and the other discharges back through it (got so hot, all the cells in the external cab welded together . . . . ).

The Prestige 1250EXT PS2E has a white or red(depending on how old it is) 4 hole rectangular socket on the back bottom left of the UPS when it is lying flat on the bench. The left end terminal is positive and the right end terminal is negative. This female socket(connector) is where the male battery connector from a Prestige battery pack will fit. It can only be connected one way. The DC battery bus is 60 volts nominal.