Place your two new type CB1270 batteries on their sides, one on top of the other in front of you with the battery connectors closest to you and with the battery connectors to your left. Connect the short (2 inch) jumper cable between the two center battery posts (1 red/1 black). Slide the battery stack into the chassis with the battery posts to your left as you face the front of the UPS and be careful that the battery posts do not touch the metal chassis. When the batteries have been slid completely into the chassis, connect the heavy red wire from the circuit board to the red battery connector at the bottom of the battery stack and the heavy black wire from the circuit board to the top black battery connector. If you have doubts about your wiring, use a DC voltmeter set to the 50v range and touch the red probe to the red battery post at the bottom of the battery stack while touching the black probe to the black battery post at the top of the stack. The reading on your meter should be somewhere between +24 and +26v depending on the charge level of your batteries.