Batteries are one of those items that last longer the more they are used. They liked to be charged and cycled every day. The longer they sit, the shorter their life will be. That is why cars that aren't used everyday end up going through batteries faster. A car battery lasting 100,000 miles on the battery is more common than a car battery lasting 2,000 miles on the same battery. This has always been a problem on collector cars. A battery tended charger is a must. Just starting your car and letting it run once a month won't help. It takes many miles after you start your car to replenish the charge lost from starting the car, and even more miles to get the battery fully charged (like driving it all day). You'll spend more money on gas than you would for the price of a battery tender.
I volunteer at a very large car museum and all the batteries on the running cars are always rotated and charged on a regular basis. Batteries are being charged every day and when you get them all charged, you start over with the first one. We have several chargers going non-stop 24-7. It is a never ending process.
Lead acid batteries thrive from being cycled and they thrive from being topped off.

Same goes for batteries in everything else you use, like cordless tools. I have tools I use and charge every other day and those batteries last longer than the tools I use once every couple months.