Here is some feedback based on my own experience and a very interesting email exchange with Chris Dodd. I have both an RWA 30.2 and a Dodd Battery Preamp.
Yes, you are going to have to replace batteries just like you have to replace tubes in tube gear. But batteries are generally cheaper and your system isn't going to get noisy as the batteries go south. The shelf life of these SLA's is several years but that is irrelevant. How long they last in your system could be just a couple of years (long playing hours at high volume every day) or many years (see Vinnie's comments). But in no case will they last longer than their normal shelf life.
Here are my personal suggestions for extending battery life:
First, turn it off when you aren't using it. For example, if you listen for an hour or two then take a break, shut it down - even if it is only for 30 minutes. If you are curious, monitor the charger light. You may be surprised how fast it fully recharges.
Second, shut it down after four hours anyway. Give it at least an hour to recharge (it may fully recharge in that time depending on how loudly you were playing it, etc.) but even if it isn't fully recharged this should extend battery life quite a bit.
Third, never run the batteries all the way down (you can't with the new Red Wine Audio products anyway but you can with other SLA powered gear). Draining the SLA's will have the same bad effect it has on a car battery - it will shorten it's life quite a bit.
Fourth, don't worry, be happy.
