Daily archives: 28/12/2018

The Nissan Leaf is infamous for its lack of battery cooling. It wasn’t really an issue on the Leaf 24, and then with the Leaf 30, you could hit the red-zone of the temperature gauge after 3 or 4 fast charges during the day. So when the Leaf 40 came out, it was with a great disappointment for the Leaf community to see that battery cooling wasn’t installed and that after just one fast charge, it could get so hot that the BMS (Battery Management System) would limit the charging speed to protect the battery. Rapidgate was born.

Why is it getting worse with the newer models?

As its name states, the Nissan Leaf 40 has a bigger capacity than the 24 and 30 but the physical size of the pack is exactly the same as the one of the previous models. When you put more energy/heat in the similar volume, heat is more concentrated and temperature rises.

Why do batteries get warm ?

Charging and discharging a battery creates heat. You can see it on your mobile phone if you play a game or use an app that needs a lot of resource/power. the battery will get warmer as it discharges. The opposite is also true, we’ve all noticed our smartphones getting warm after a long fast charge. The exact same applies to car batteries. When you plug at home and draw 3 or 7kw of power, your battery will not suffer from excessive heat and it will stay at a reasonable temperature level. On the other hand, when fast charging at 40 or 50kw, the battery will get very hot, very quickly. Batteries are usually happy around 25-30°c, this is why most manufacturers offer battery cooling/warming. This is best for a better battery life. In parts of the world where climate is hot, such as south California or Arizona, Leaf owners have seen their batteries degrading very quickly. Thankfully, we have an extremely mild climate in Ireland, never hot, never cold, which minimizes the issue, and making our country probably the most EV suitable in the world 🙂

So what can I do to to keep my Leaf 30 / Leaf 40 battery as cool as possible ?

If you know you are driving a long distance in a day (say 400km or more) there are some simple steps you can follow to limit that heat gain:

• Fully charge your car the day before. It sounds obvious, but charging the car the day before, allowing the batteries to cool down after the charge, will allow you to start your journey with a battery as cold as possible. The battery being full, you’ll make your first fast charge late in your journey.
• Drive at reasonable speeds. The faster you drive, the worse economy you will get. A car doing 16kWh / 100km at 100kph will draw 16kWh in one hour. A car doing 12kWh / 100km at 80kph will draw 12 kWh in 1 hour 12 min so less than 10 kWh in one hour ! More time between charges mean your car will be able to naturally cool down a little. A better efficiency will allow you to get more kilometers from your charge and, spend less time recharging ie put less heat in your battery.
• Accelerate gently, use the Eco mode to help you doing so.
• Avoid regeneration. Every time you slow down, you are recharging the battery and adding a bit of heat back into the battery. It is better to avoid it as much as possible. If you’re cruising at 90 kph on the motorway and that it is going downhill, just coast and let the car pick up some speed, rather than regenerating. On a Leaf, you will need to press slightly on the accelerator to do so.
• Do not use cruise control. It doesn’t anticipate slopes as well as a human can and will therefore over-accelerate and over-regenerate.
• Minimise the use the e-pedal (ideally deactivate it): it is a very good system especially around town but has a very strong regeneration that of course will produce heat.

Finally keep in mind that driving slower will not necessarily mean arrive later at your final destination. If you drive faster between 2 charges and save 20 minutes by driving 110 kph instead of 90 kph between 2 charges, you could loose much more than these 20mn spared by spending more time at the FCP. A Leaf with a cool battery should take around 45mn to charge 80% at 50kw but this can easily double if the battery is hot and charging speed slows down to 22kw as seen after 1 or 2 fast charges. Drive wisely !

Edit (28th January 2019) : Recently, Nissan has updated the software dictating the speed at which the car must charge (based on the battery temperature). It seems that this fix is only for Europe and will be also carried out on existing Leaf. Tests have been done and it seems that the car charges faster at any temperature, which is a help on longer distances. However it means that the battery will get more heat thus challenge its life expectancy.