Here's the unvarnished truth about batteries....
1. There are on-line stores that sell batteries by physical size. If fitting the battery box (physical size) is important, then you can try a source, like
Battery Jack. Look under "motorsports" because a mower battery is most like a car or motorcycle battery.
https://www.batteryjackdealer.com/
2. The factory installed the cheapest battery that met the requirements. So it doesn't make a toot what brand came with the mower. You probably can't buy that brand anyway, unless you buy batteries by the pallet load. You simply need a battery that meets the requirement specs.
3. Batteries are NOT like other electrical devices. I once worked in an OLD house. The Edison light bulbs from the 1920's in the attic still worked ! However, because batteries are liquid
chemical devices they are not like light bulbs. They are subject to electrical charge, age, temperature, local environment, etc, etc. In other words they are more like owning a dog in that they REQUIRE
regular attention and maintenance.
IMHO, the
Interstate Battery is the best you can buy. But, if you bring home the very best, $3000 pure-bread dog, but never care for him... he'll soon be dead by starvation, disease, loneliness, eaten by coyotes, rabid raccoon attack, etc, etc. So don't tell us the brand of battery, instead tell us what care you gave the battery. I suspect the answer is "None", and so, like the dog, neither of us should be surprised that you are once again back at the battery store doing more shopping.
Basics
A. Most batteries are now made in China and quality is way down. So if you expect even a moderate life, then you had better be "loving on them" like a pet.
B. If there's a water level, then you need to watch that level and add distilled water when needed.
C. Battery posts need to be clean and corrosion-free at all times. That means being pro-active with anti-corrosion battery post treatments.
D. Batteries need to be maintained YEAR-ROUND in a charged state, and protected from freezing temps. The best way to charge a battery is to run the piece of equipment. Second best is to disconnect one battery cable during any storage
*. Third best is to attach a sub-1A "trickle charger" for ~3 hours, about once a month. (Too much charge is worse than too little.) In a perfect world, you might have one battery which you put in your mower in Spring, put in your motorcycle in Fall, and put in your snowblower for Winter.
E. BOTH battery cables need to be in A+ condition and there can be NO corrosion or rust at either end.
F. The ONLY test of battery condition is a "battery load test".
* I'm a huge advocate of these battery disconnect devices.
CLICK HERE
Hope this helps.