Deep cycle lead acid can last a lot longer than that with shallow cycling, intelligent charging and the use of a desulphator. Mine are over ten years old now, work fine. They've lasted that long because I never beat on them.
Telco exchanges had/have big aquarium looking lead acid backup batteries that lasted twenty years then tons got sold off cheap to enthusiasts where they were put into service for the earlier adopter off grid solar guys. This is *old* mother earth news and home power magazine info, and the battery subject has been looked at in depth by literally hundreds of people, and year after decade lead acid still rules for the cash involved for large applications, until you get to utility scale, where it is pumped water storage and turbines, etc.
Lead acid is still the king for stationary storage purposes when it comes to amp hours/dollars, for home use. I seriously doubt that lithium ion will come close for a long time, I mean, look at what replacement cellphone and laptop batteries cost.
And how many just car starter batteries do we see at whatever*mart or the auto parts stores that use lithium tech yet? Yep, about zilch, people don't want to spend a thousand bucks for a starter battery. There are still some advances in lead acid out there, the most common you see for cars is the spiral system from Optima http://www.optimabatteries.com/home.php , and the Firefly company http://www.fireflyenergy.com/ is allegedly going to start having more fleet sales "soon" with their lead "sponge" tech, and perhaps eventually normal retail.
The cheapest locally sourced way to get lead acid today that I have found is to look around at forklift stores and get an electric traction battery pack @ 12 to 48 VDC (probably other voltages as well, haven't looked for awhile now).
They are *heavy* and come in steel cases with lifting points and welded bus bars.