I’ve got an SSB LFP7L-B in mine, which is probably overkill.
It’s a lot shorter than the stocker, so it needed a couple of spacers underneath, which fortunately came with the battery. Otherwise it would have been some scrap styrofoam.
I’ve also fitted a “modern” reg/rec, which keeps the charging voltage in order. It’s a stock unit from a 1989 Honda CBR250R, but apparently first-generation R1 reg/recs are the easiest upgrade for those things, so go Yamaha if you haven’t already upgraded.