Battery

As we all already now that batteries main problem is that they tend to discharge too fast. There's never not enough energy. But technology, electronics and machines tend to develop and use more and more power. Seems like batteries are just a little bit behind in development, but it makes all the difference.

Battery changes electric energy into chemical energy and stores it until someone connects a load to it and then it starts to change stored chemical energy 
into electricity on its plus and minus terminals.

Batteries use to be measured in amphours Ah it meant how many amperes in one hour you could get from the battery. 
Its ok to use it on a usual ICE car starter battery because they mainly are 12Volt batteries. 

 On electric cars its not very often so, only BMW is using this at the moment (2020) on their only EV BMW i3. 
 Now they offer 120Ah battery for the car but when they started to sell this model (in 2013) it had half the capacity 60Ah. 
 In a few years batteries have gone twice as better! 60Ah is 22kWh and 120Ah battery is 42kWh.

To describe batteries on EV-s is mainly in use unit kWh kilo Watt hour. This is unit for measuring electric energy and it fits 
much better with cars since they use a lot of energy. Kilo Watt hours is also used to measure home energy consumption. Only difference is that you multiply Volts with Ah and you get Watt hours if there are many of them then you will use prefix kilo.

For example New 2020 Nissan Leaf you can buy with 40kWh or 62kWh battery. The biggest batteries on road cars are right now 100kWh Tesla model Y. But allready manufacturers claim that there will be EV pickup trucks with 200kWh batteries and so on.

Theres electrical safety and physical safety. Physical safety means keeping the battery in suitable temperature range mainly Lithium batteries are best at 20C but some heat them up to 40C to get better fast charging speed. Theoretically they say that lihtium batteries do not like charging in cold under 0C. But older EV-s had these situations in winter and they worked fine. Nowadays (2020) batteries have liquid heating and cooling systems to keep them in the best temperature region.

Theres also high voltage risks, for example big crash and high voltage orange wires will be revealed. In that case EV control system will switch high voltage system off. Also there is new danger in the car workshop where technicians need to be trained to service and fix these cars.
Crash tests are performed to design and make safe case for the battery. Same as with petrol cars where is flammable liquid in the petrol tank.

Batteries need to be taken care of not to overcharge and undercharge. Nowadays 400V EV batteries consist of 96 cells connected serially. Each serial cell voltages are monitored that is the job of BMS

Battery monitoring system (BMS) or Nissan names it LBC lithium battery controller. Takes care of battery “health”. EV battery has to last for 10 Years and to fulfill this expectation there is a bunch of electronics and clever software.