That's totally true. I started using battery tenders, & they make a huge difference. I use them on my Subaru (when it sits for a long time), UTV, ATV, Compact tractor, & riding lawnmower. I even throw a battery tender on my newer Mirage if it's going to be an extremely cold night (-20F for example). Thank goodness - my three chainsaws, log splitter, push mower, gas powered weed wacker, & rototiller don't all have batteries, too! :)
The riding lawnmower batteries that I am thinking about are noticeably larger than the stock battery in my Mule, & they are about half the price most of the time.
Walmart motorcycle batteries have crapped out on me relatively fast. Those from AutoZone or Farm & Fleet have done much better for me, too.
These are some examples of the stock battery choices -
https://www.batteriesplus.com/batter...4x4/400cc/2008
https://www.farmandfleet.com/product...t-battery.html
I want to go with a standard basic lawnmower battery -
https://www.farmandfleet.com/product...s-battery.html
These standard batteries are stockpiled most everywhere & they are much cheaper. Others who own side-by-side have had this same discussion.