i'm a keen mountain biker myself, E-Bikes are getting more & more popular although personally i 'm not keen on them. But for a decent e-bike from a reputable brand within the mountain bike scene, you're looking at £2k plus. But like everything nowadays, china has their own cheaper versions of E-Bikes which are very cheap....for a reason! ..almost every week i'm reading on forums about batteries exploding (just like this) belonging to Chinese "copy" e-bikes! But to be honest it ain't just e-bikes.. For years there's been cheap batteries available for all our devices which are NOT safe, but because of the price compared to genuine batteries, its hard for people to say no.
But difference between a mobile phone battery & e-bike batteries can be 50+ volts (as technology advances the voltage on e-bikes will just keep getting higher) ...when a mobile phone battery decides to self explode, i'm sure we have all seen videos on the net what happens...for a small battery it can be pretty devastating, but when one of these e-bike batteries go up, they are basically like a flame thrower/small bomb!
But if i was to ever by an e-bike (very doubtful!) it would definitely not be a cheaper Chinese copy, because basically your just sat on a time bomb ticking away right below your nads!!