There are huge variations in the quality of e-bike batteries.
Cheap Chinese cells and poor Chinese assembly, crappy battery management electronics, and also batteries which have been dropped or crashed or otherwise damaged are all potential hazards.
A e-bike shop in Chinatown is just where you expect something to eventually explode into flames. And when they burn they are near impossible to put out.
I have two e-bike batteries, although Chinese made they are from a reputable manufacturer, have a good control system, and use Korean (Samsung) cells.
I still only charge/keep then in the garage and I don’t bring them in the house.
I don't need to tell you because I am sure that you are already aware, but for others here...
I have been buying Chinese Lithium-Ion batteries for many years mostly 18650 cells that I use in flashlights, etc... I have never had one of them catch on fire. But I have had some difficulties with expensive Lithium Polymer batteries from toy drones where they again didn't catch on fire but produced some nasty smoke when they overheated. Fortunately, I was using them outside and was able to remove them before they destroyed the drones. Those batteries are designed to be light weight and capable of high discharge rates.
I use some sophisticated charging equipment with these types of batteries that helps to monitor their condition. Any batteries that I suspect might become a problem are charged and stored in a large, detached outbuilding on a concrete floor far enough away from flammable items and debris that if there is a problem when they are left unattended that a fire would be unlikely to spread.
https://www.androidauthority.com/lithium-ion-vs-lithium-polymer-whats-the-difference-27608/
We have rechargeable lithium batteries in so many items these days. Most of them are well designed and pretty safe, but there is a reason for the shipping labels that we find pasted on boxes when we receive electronic items through the mail or delivery services.
The batteries that are found in items that are designed to be light and capable of high discharge rates such as e-bikes and radio-controlled toys are a little different animal than batteries found in phones and computers. The same is true of the high-capacity batteries found in electric cars.