Just replaced the one on my '15 RT a little more than a month ago. It was a preemptive replacement, since the original battery was still in excellent condition. I went with a Yuasa GYZ16H, and paid around $85:
https://www.walmart.com/ip/YUASA-GYZ16H-FACTORY-ACTIVATED-MAINTENANCE-FREE/129243723
This battery will fit in the battery compartment perfectly, even if it is not as tall as the original battery by almost 1". It has a higher power rating than the stock Exide battery, at 240 CCA vs. 220 CCA for the Exide, but I am going on memory for the Exide number.
IF you (or anyone else) decide to go with this battery, I have a hint regarding installation, that will make life very easy for you! The hint has to do with the connections to the Yuasa battery terminals. On the stock Exide battery, you will find that the connections are bolted directly into a tap hole in each terminal. The Yuasa battery has a "hollow" terminal, and you are provided with a pair of nuts, bolts, and washers. The nut is supposed to go inside of the hollow terminal, and you have to hold it up against the top inside surface of the terminal while screwing the bolt into the nut through the clearance hole. Much easier said than done, with the extremely limited space and thick finger! Here is the hint. Take a strip of paper and fold it up to make a flexible spacer that you place under the nut, to hold it in place against the inside top surface of the terminal. Now, you will have both hands free to hold the short bolt and the power lead, while screwing the end of the bolt into the nut! Worked perfectly!
PS: if you go on Yuasa web site and do a search based on bike make/model/year, you will find that Yuasa will recommend 3 batteries option for our bike. The lowest rated option has the same electrical specification as our stock Exide battery, while the option that I went for has the higher CCA rating, and is delivered fully charged from the factory. The 3rd option is with a model that is physically and electrically the same as the one that I picked, but it comes with an acid pack that you need to put into the battery, and then charge the battery yourself. The last option will give you the "freshest" battery possible!