Yamaha charging $2475.00 for a battery

$299 battery. Lots of corners are cut to produce a battery at that price. Junk. And exactly the sort that is responsible for fires. Period.
FWIW, from what I see an Aventon battery is actually $500. Which is on the less expensive side for proprietary batteries but not insanely so. It looks like they will knock $200 off the price of a spare if bought with certain bikes, but that doesn't mean its actually a $300 battery.
Something that I found when I was building my mobile charging kit. The original wire I used because I didn't think about it was CCA (copper clad aluminum), which as an interesting and annoying property. Since it's aluminum at it's core, it has a higher resistance than copper. Also, as it gets hotter, it's resistance increases causing it to draw even more current causing it to get even hotter. Eventually it would get to the point where it wouldn't blow the fuse, but would melt down the DC accessory plug.

I changed over to pure copper wire and haven't had any problems like that since. I have to wonder if some of these battery packs are using CCA and getting melting down because of it.
I saw that 2400 dollar Yamaha battery on sale at an on-line bike shop in California, likely where the OP here found it and got the shock of his/her life.

1200 seems the going rate for the internal Yamaha battery; a few hundred dollars more than what I paid for my spare external Yamaha batteries for my Haibike. If you want to go Yamaha.......or Bosch........or Specialized.......or Shimano, you pay the price for entry into that brand. No way of getting around it. The good thing is the Yamaha batteries are long lived with very little issues noted on this forum site for all the years I've been reading it. Do know that they cannot be rebuilt, no battery rebuilder will touch them as the BMS, once it is "awakened from it's slumber sleep", cannot be disconnected. If it is, instant brick. "Proprietary parts for the motor itself, or control buttons or displays, are easily attained through PartZilla as noted earlier. You just need the right part number to find it.

I'm partial to the Yamaha motor as it powers the only Ebike I've owned since early 2017. No problems worth noting here in almost 20k miles.