This is true. I do it all the time. As long as you ensure the batteries are the same voltage, use the same F1 or F2 terminal, and have the same physical dimensions so they fit inside the battery compartment, you can replace the batteries with higher Amp-hour capacity cells. The result is indeed longer battery run times. If the connected devices ran off DC, those higher Ah cells could deliver more power too. But that is limited by the UPS circuitry to prevent excessive current situations - a good thing. And while possible, it is not a good idea to use less capable cells. That is, if your UPS typically uses 12 9Ah, it would not be wise to use 12V 7Ah cells as that will decrease the VA capability significantly. Depending on the load, it could result in the UPS shutting down prematurely, or fail to cut over to battery at all. I run all my network gear through my UPS too. If there is an outage, and if I am quick to shutdown my computer and monitors, my 1500VA UPS will keep my network alive for at least 6 hours. This is great since that means I still have Internet access and communication to the outside world with my other portable devices (laptop, cell phone, ect.) - at least until their batteries run down. You don't have to go with deep cycle batteries. Standard SLA batteries work just fine. Deep cycle batteries are typically found in scenarios where running the batteries down to discharge (or near discharge) is a common, almost daily occurrence. For example, when used in wheel chairs, or outdoor lighting that come on at night and off at dawn, then charge with solar power during the day. In most UPS scenarios, they typically go many days, even weeks or perhaps months before kicking over to batteries. And the typical scenario then is they only run for a few minutes before power is restored, or the user shuts everything down. Just looking at my APC PowerChute logs for the UPS on this computer, in the last 24 weeks, my unit switched to full battery backup just 3 times, with a total time of 45 minutes, 11 seconds on battery. If I remember correctly, one of those outages lasted about 30 minutes and the other two I don't remember, but clearly, only about 5 minutes each on average. Now there is a note that says, "Power problems of a very short duration are not recorded here." My documentation does not say what "very short duration" means but I believe it is 1 minute or less. So even though I live in Tornado Alley and my utilities drop from poles instead of being buried, you can see where "deep cycle" batteries are not necessary - at least not for me. Note too that does not mean my power grid is stable. On the contrary, little "flickers", surges, spikes, dips and sags are common. That's where the AVR kicks in.