"The mta has to prove, to themselves that they can do this...

"The mta has to prove, to themselves that they can do this safely, without the battery heating up to possibly the point it catches on fire and it will be able to be recharged how many times'

Maybe depends on how the battery pack is configured ie in the the case of the latest Tesla 3 car the car has close to 5000 individual batteries each battery is connected to the circuit via a fuse wire , and glycol antifreeze runs in pipes down between the rows of batteries .
Having so many batteries in itself is a safety feature due to the large surface area to volume ratio to dicipate heat .
If an individual battery short circuits internally and overheats it will burn out the fuse so the possibility of a chain reaction will not occur .
If the batteries discharge fast causing heating then the glycol circulating is cooled down by a fan , they glycol also is the car's cabin heater .
THere are around 1/10 th as many fires with Tesla cars compared to ICE cars , however there is an urban legend that Tesla cars catch fire regularly
There is still the possibility of auto fires , but it is mainly from an accident where a foreign source causes ignition , after the battery pack has been broken ,- similar situation to a ruptured car fuel tank.