Do you mean how long will they last? Typically, 3 to 5 years. Again it depends on usage, what you expect from them, and how well they are maintained. Have you checked the water in them lately? 30 minutes will not charge them properly, need a good 3 stage charger and at least 3 days plugged in to charge them properly. They need to be used occasionally, so camp one night with just the batteries, but have shore power to recharge them with the next day.
It's kind of like most everything else, "your mileage may vary"
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT