You can read all sorts of things about electric vehicle batteries everywhere. There are those who rely on their computers and cell phones and believe that an electric vehicle battery will need to be replaced within five years, and others who believe that a battery doesn't need any maintenance, as if oil changes in a gasoline engine weren't really necessary. The truth lies somewhere in between.
Battery composition
Not every battery is the same. Manufacturers have chosen different recipes, and the results are not the same. Panasonic uses a Nickel-Cobalt-Aluminum process with a thermal system to keep the battery at a stable temperature. LG Chem has a Lithium Polymer system with a thermal management system, then Samsung SDI uses Nickel-Cobalt-Manganese, again with a thermal management system. AESC manufactured Lithium-Manganese Oxide batteries without thermal management. Of all the manufacturers, Panasonic seems to have the best recipe, the worst being AESC. 1
How does a battery degrade?
Before discussing the required care, we need to understand how a battery degrades. We lose autonomy, yes, but what happens inside? In fact, the battery degrades because microcracks appear on the anode and cathode, and then some of the ions remain in these cracks. In addition, the surface of the cathode becomes larger with the accumulation of residue, and then the same thing happens on the anode side, which is called dendrite, until the two parts join and cause a short circuit.
What affects battery life?
So, a battery is doomed to die. Like humanity, each battery will have a completely different lifespan from another. Battery chemistry, thermal management system, or lack thereof, and charging management system can greatly improve battery life.
Coulombic efficiency
One of the best ways to check battery health is to check the Coulombic efficiency. During charging, lithium travels to the anode and then returns to the cathode during discharge. Between the two, there is a variation in the transfer, and this is what is analyzed. Through various tests, it has been determined that three factors appear to greatly affect battery life: heat, charge rate, and the number of recharge cycles. 2 
How to extend battery life
According to several experts, these three factors should be avoided as much as possible and, above all, not combined. Regarding the number of charging cycles, it is recommended to do short recharges rather than one long one. The heat generated during charging will be shorter. It is therefore better to charge at a 240-volt station rather than at 120 volts. Fast charging, those performed on a level 3 charger, should only be done when traveling. Here again, the heat generated by charging is the culprit. It is said that high voltages and exposure to high temperatures degrade the battery more quickly than charging under normal conditions.
Also, an external temperature higher than 30 Celsius and lower than -20 Celsius is considered an extreme temperature. Therefore, it is important to ensure that the vehicle can warm up or cool down properly. Most vehicles do this with a pre-set battery level, but if the vehicle requires plugging in to do this, it is a must.
Next, you need to maintain a voltage of 4 volts per cell to ensure a good lifespan and range of use. This value is obtained at around 70% of the charge. On the other hand, a value lower than 25%, or 3.65 volts, is not recommended. These values are valid for daily use or for a vehicle in storage for a few days. However, if you need to recharge to 100%, do so as close as possible to your departure to minimize the time generated by heat in the cells when they are fully charged. 3
Usage range before recharging.
The figure above illustrates dynamic stress tests reflecting capacity loss at different charge and discharge percentages. The greatest capacity loss occurs when discharging a fully charged battery from 100% to 25% (black); the loss would be greater if completely discharged. A cycle between 85% and 25% (green) provides a longer life than charging to 100% and discharging to 50% (dark blue). The least capacity loss is achieved by charging the battery to 75% and discharging to 65%. This, however, does not fully utilize the battery.
In conclusion, it's best not to charge your battery to 100% every day or to schedule charging to end as close as possible to your departure. It's also advisable not to leave the vehicle in extreme temperatures unless it can cool the battery. Since the Nissan Leaf and Volkswagen EGolf don't have thermal management, only a battery heating system, avoid high temperatures. Also, unless absolutely necessary, avoid fast charging, especially if you don't have thermal management.
I invite you to consult the links at the bottom of the article. All information contained here comes from this verified and verifiable information.
1 – https://batteryuniversity.com/learn/article/bu_808b_what_causes_li_ion_to_die
2 https://batteryuniversity.com/learn/article/bu_808c_coulombic_and_energy_efficiency_with_the_battery
3 – https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
