The vast majority of batteries in phones/laptops are safe and comply with various mandatory and elective safety standards. The e-bikes most commonly purchased do too. But many people buy cheaper batteries or run more amperage through them than is sound, and you get bad results.

There are plenty of incidents with “thermal runaways” in consumer batteries too — next time you’re on a plane, pay attention to the new addition to the safety briefing about not retrieving your phone if it falls into the seat. That warning is because of what happens if you crush a phone (it’s a battery fire)