What type of Converter / Charger do you have and are you sure they are getting a full charge from your Converter / Charger?
The above advice should be followed but you do want to make sure Charger is doing it's job.
Also, I replaced the stock WFCO Converter / Charger in my coach with a Progressive Dynamics model that has an Equalization Mode that kicks in every 21 hours for a period of 15 minutes with a voltage of 14.4v to prevent battery stratification & sulfation, which is the leading cause of battery failure.
Progressive Dynamics uses 4-stage system microprocessor technology to add intelligent charging capability. It constantly monitors the RV battery and automatically adjusts the converter output voltage based on the battery’s charge status – designed to eliminate battery over & under charging problems associated with most other battery chargers and provide rapid yet safe battery recharging after dry camping.
I also use a Solar Charge Controller that also has the Equalization Mode.
If you make an investment in good deep cycle batteries and you want them to last and give you the best possible performance, I would also look at making sure your Converter / Charger offers the Equalization Mode.
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