I've got 5 years on my rv batteries without solar but if you believe everything you read on the net, were both lucky.
This is about solar batteries.
Car batteries are not recommended. Yes, they are cheap, but car batteries are designed to discharge a lot of energy at once and then recharge slowly, while a solar setup needs just the reverse --- a battery that will recharge quickly and discharge slowly (known as deep cycle). Experts say you'll get a few months of life out of a car battery hooked up to solar panels, but that's it.
RV or marine batteries are the next cheapest, but still aren't recommended by experts. They're usually easy to find locally and they do last a bit longer than car batteries, but probably will die within a year. They also have a tendency to explode if not cared for well.
Golf cart batteries are considered the minimum acceptable batteries by solar experts. They are generally 6 volts, so you'll need to buy them in pairs and wire the batteries together to create a 12 volt system. Golf cart batteries usually last two to four years when connected to solar panels, and one site claims that Deka batteries will last 5 to 10 years and another lists Trojan T-105 batteries with the same cycle life.
Gel cel or absorbed glass matt (AGM) batteries make it easier to design your battery box since they don't need to be refilled and don't vent explosive gases, but they cost about 30% more than a similar capacity golf cart battery and don't last any longer.
Fork lift batteries --- Only one website mentioned these batteries, but the author glowed over their life expectancy. Otherwise, they're similar to golf cart batteries, only much more expensive.
