To make your battery last longer buy the most powerful one you can find (that will fit). A larger battery that barely works to start your engine will last a lot longer than a marginally sized battery that has to give everything it's got to start your engine. Rule of thumb 25 years ago was 1 cold cranking amp for every cubic inch engine displacement, nowadays, you can easily find batteries that are double that, and they last much longer. Cost difference for the more powerful battery is insignificant as the cost is spread out over many years, and the larger one will outlast the smaller ones by a wide margin.
While we are talking about batteries, I use only large regular (not deep cycle batteries) in my motorhome for the engine and house batteries (MH has only 1 house battery). Deep cycle batteries, the largest ones I could find were lasting about 18 months and had a 12 month warrantee. Large regular batteries are about ten bucks cheaper and last about 4 years in my case--and usually have a 3 year free and 7 year prorated warrantee.