'04 Battery Recs?

Bought an '04 Rebel as my first motorcycle a couple weeks ago, it bump starts super easily and runs just fine but if I use the starter button it either weakly tries to start or just clicks. Seller stated the battery was replaced last year but the bike was barely ridden and that the heat kills small batteries, so he always bump starts it when cold but once hot, it will start off the button fine. He demonstrated this but I haven't been able to replicate it. Skill issue? Possibly.

My understanding is there's no point in testing the charging system without a fully charged battery and I like to put new batteries, oil, etc in new to me vehicles for a clean slate so I'm battery shopping. Looking at Yusua and wondering if there's any reason not to go that route.

Alternately/additionally, I guess the starter could be bad. It sounds just like my car would if the battery was dead so the starter isn't my first suspicion but if it is the issue, eh, whatever, it's a 20 year old bike. Not a total shocker that something needs replaced 🤷

Total aside: Does anyone have any sources for OEM service manuals?