at the very least, a powerhead and an air pump in each display tank. i use a UPS that has only one of my return pumps on it, and will run that pump for about 45 minutes. if power is out longer than 30 minutes after that battery is spent, i crank up the little 1000watt generator and run the return pumps and the skimmer pump - no lights or anything else. i dont know how long anything would live if nothing were done, but i am not about to try and find out either ;)