Another option is using a combination starting/deep cycle battery. I have had very good luck with AC Delco Voyager Marine/RV starting /deep cycle batteries - they usually last me 4-5 years. As long as the battery has plenty of juice to start your engine, using a battery with some deep cycle capability can be a good thing. A single Group 27 Voyager battery has proven to have enough oomph to start both a 1980s vintage Evinrude 150 and a 1990s Yamaha 150 on different boats, for
years. I've always got the second battery for backup, even though I haven't needed it.
The advantage of using a battery with some deep cycle capability is that you won't kill the battery if you leave something on that runs the battery way down. I've accidently done this a few times over the years and the Voyager batteries are fine after being re-charged. If you do this to a straight starting battery that's a few years old it's a lot more likely to kill the battery.