Why does my mechanic say 60Ah when my old battery label says 55?

Last Tuesday my 2017 Kia Sportage would not start in the underground parking at my office, and by lunchtime a mechanic had confirmed the battery was finished. He told me “you need a 60Ah,” but when I looked at the faded sticker on the old one, I thought I could read 55. I asked him why the number was different, and he just said “close enough, 60 is better.” That answer did not satisfy me, so I started asking around. My brother says a slightly bigger number is always safer, especially with the AC running all day in this heat. My neighbor says the Ah number is only one part of the story, and that the size, the terminal side and the starting power also have to match the car, or the battery will not sit properly in the tray. A friend at work told me he bought one with a higher capacity than the original and it fitted fine, but another colleague said the charging system in some cars is made for a certain range, so a much bigger battery may never fully charge on short trips. I read a page on last night to understand what the number means, and it explained the capacity, the dimensions and what to check against the car, which I wrote in my notes. Since my office is near DIFC, I have been looking for a Certified 60Ah battery replacement near DIFC, so I can ask them to compare the new battery with the old one before I pay. My questions are easy. Is it okay to go from 55Ah to 60Ah, or should I stay with the original number? How can I check the terminal side before the old battery comes out? Should I ask the shop to show me the date code on the new one? And does a slightly higher capacity really help in summer, or is that just a selling point? Please share what you chose. Thanks for reading.