Lauren … I always use Odyssey batteries. They are not cheap, but in batteries, I believe you get what you pay for. The PC680 Odyssey for my RT is $129 on Amazon. https://www.odysseybattery.com/ . Mine is on it’s 6th season this year.
The secret to battery longevity is to have it on a battery maintenance charger whenever you’re not riding the bike. This is the one I would recommend ….
http://products.batterytender.com/Dion/Battery-Tender-Junior-12V-0-75A.html . Amazon has it for around $25.
No mater which battery you get, keep it on the Battery Tender.