I just recently installed a 1.5k inverter/charger with two batteries in my apartment. The inverter and batteries were actually installed outside the apartment under a protected area with wires running over the roof and down the pipe to the breaker panel.
Plaza Llama in SDQ had a sale on the inverter & battery package that included installation for around 19000.00 pesos. It will run the basics; lights, fans, TV, stereo but not the refrigerator. Sure beats sitting around in the dark!
You can buy ready made frames to hold the batteries. The frames are bolted to the wall near the inverter and have provision for a padlock. Most hardware stores seem to sell them. A four-battery frame runs around 1000.00 pesos.