eBay & Alibaba & Ali-xPRESS then DHGate some even now on the .com of Walmart.
Applications include AUTO then e-Bike & Solar. plus many many others.
I have seen Nissan & other such Batteries as Used but Working for relatively cheap on eBay. Myself I buy e-Bike Batteries mostly from that same Site. That is one of my e-Bikes that I build & use in place of Auto. That frame is Titanium direct from China. TheTri-Spoke Magnewium Wheels are real sturdy. That Red Cart in the Green Light is my Solar Cart. Bottom 2 LIFEP04 Batteries 48v 20ah & 36v 30ah. Then the 36v 1500w Sine Wave Inverter & Chargers for e-Bikes & Solar Chargers on top.
The Batteries usually someone has a specific intent in mind by saying directly & specifically one kind of Battery. Li-On is specific to certain uses mostly. LiPo more vast but similar & then the others. I have 18650’s I use alot w/ like Li-Mn eFest Purples then Panasonic NCR18650B they have like 10a top discharge. IMREN they have certain Chemistry. Those are what is in alot of batteries just cased.
Some LiPo are like built into certain items. Replacing them can be a challenge some are like lead in how they feel & look. Sort of malleable but encased.
If you Research your Battery find it then check the Seller higher ratings on like eBay mean better communication possilby. Contact the Seler wherever you buy ask questions you have. If they don’t write back it might be a good idea not to buy from that particular one. i have learned some key things from great questions.