In what may be great news for 40 kWh Nissan LEAF owners, a software update evident in newer LEAFs has alleviated much of the #rapidgate DC charge throttling issue, allowing reasonably fast DC charge rates even if the battery is already hot.
This initially appears to be a software-only update, without any hardware fix, suggesting that Nissan is confident that allowing somewhat hotter batteries will not be a significant problem for battery longevity. It is not yet known for certain whether early-production 40 kWh LEAFs will be able to get the software update, but it looks positive.
As we covered extensively earlier in the year, owners of the 40 kWh LEAF who attempted to drive the vehicle on long journeys with 2 or more back-to-back DC fast charges were disappointed to find significant charge rate throttling on the 2nd and subsequent charges. The throttling occurred whenever the battery was above 32° Celsius. This charge throttling was designed into the software by Nissan, in order to prevent excessive heating of the battery under repeated high-power DC charges.
This was deemed a necessary step by Nissan due to the LEAF not having any active thermal management to cool down the battery during high power throughput. The only solution was to reduce DC charge rates as the battery reached higher temperatures, to reduce the possibility of damage due to further excessive battery heating.
A frustration for owners was that, in many cases, this limitation in multiple DC charging was not made clear to them in advance of purchasing the vehicle. The UK advertising standards authority even ruled against Nissan’s original marketing approach for the 40 kWh LEAF, for omitting clear information about this limitation.
A Software Fix
There have been discussions on LEAF forums over the past week or two since some informal testing of newer LEAFs suggested a software update had been implemented. The new software adjusts the charge throttling behaviour, as initially demonstrated in a video by Electric Swede on December 22nd.
Over the past 24 hours, Bjørn Nyland has done a more complete test, and has generated solid data that confirms that the new software has indeed changed the charge throttling behaviour (see especially the final 20 minutes of Bjørn’s video). It should be noted that Bjørn’s test was done in the Norwegian winter in ambient temperatures of 0° to -10° Celsius, but his data show a very significant improvement over previous results in identical conditions. It will take some time to learn whether the software will also allow the same magnitude of gains in warmer ambient conditions.
Here’s a graph of the original charging curve, with a rough trend line (in red) connecting the three new data points that Bjørn recorded:
As we can see, peak charging power at moderately hot battery temperatures has been boosted by 40 to 50% or more, meaning that owners should be able to experience decently quick 2nd and 3rd DC charges, adding 70% SOC (from 10% to 80%) in under an hour, so long as plug-in temps are not over 50° Celsius.
On the previous software, plugging in at 41° Celsius (a common battery temp after one DC charge and 2 initial driving stages) would have required 54 minutes to recover 70% SOC from near empty. With the new software, the time for this scenario is reduced to just under 40 minutes, so a significant difference, and more in line with the LEAF’s EV peers.
Plugging in at 45° Celsius, the improvement appears to be a reduction from 72 minutes (old software) to 48 minutes (new software). As usual, moderate driving speeds and avoiding high acceleration are still the best practice for taking care of battery temperature (and thus optimising your charging rates) during a long trip.
Cautions, and Look out for More Information
Obviously, the new software results in higher battery pack temperatures, and we don’t yet have Nissan’s explanation for how this will (or will not) affect battery longevity. Since Nissan will likely be keeping the same battery warranty terms, we can conclude that they at least feel confident that longevity will not be a significant issue.
We also don’t yet know if the charging curve has been tweaked to be gentler and somewhat flatter, avoiding unnecessary heat generation from peak power, or any other specific details. What’s important for now is the end result — much improved DC charging times.
We should find out soon whether the new software update will be made available to older 40 kWh LEAFs, or whether a tweaked battery chemistry or hardware only available in newer LEAFs (e.g., less internal resistance and/or more heat tolerant) is the basis for the software change. Let’s hope it can be rolled out to the early 40 kWh LEAFs.
We will have to wait for data from hot climates to see whether practical gains to charging speeds occur even in high ambient temperatures. Don’t expect miracles. For the many owners in temperate climates, this software update has the potential to transform longer trips, effectively removing excessive recharging delays on a journey that requires 2 or even 3 rapid charges.
If you have spoken to your Nissan rep about this, or have other solid information, please share in the comments below.