Test Results on Battery Health

[joeriv]

I found two lab studies which may shed some light on Nissan's battery degradation and conditions for maximizing battery life:

https://avt.inl.gov/sites/default/files/pdf/vehiclebatteries/FastChargeEffects.pdf

This study follows four Nissan Leafs over a 50,000 mile test, two cars which were DCFC charged and two which were L2 charged in Phoenix AZ. The cars were run 6 days a week almost to turtle and then immediately charged to full. Ambient temps were what you would expect for Phoenix and contributed greatly to battery loss - marginally worse would have been Death Valley. Average battery temps during charging ranged from 73F to 105F.

The average of 3 different measures for battery capacity remaining after 50,000 miles showed 74.5% for L2 charging and 69.8% for DCFC charging. These results are absolutely worst case conditions for the Leaf.

http://batteryuniversity.com/en/learn/article/how_to_prolong_lithium_based_batteries/subscribe_thx

This study on prolonging lithium battery life verified what many of us believe:

1. Heat is the worst enemy for lithium battery life.
2. Deep cycling hastens battery degradation.

One conclusion of this study was that charging between 65-75% State of Charge (SOC) offered the longest life cycle, maybe not realistic for EV batteries, but instructive nonetheless.

My takeaway is that keeping my Leaf battery between 35 to 75% SOC at moderate ambient temps will add a lot to battery life. Thankfully temps in CT are not anywhere near Phoenix levels during the summer.

No doubt there are some cases that are more extreme under less trying conditions - that's why there are two tails on a normal distribution curve; some will show incredible longevity and some will degrade faster than average. That's just the nature of the beast.

 

[LeftieBiker]

Do they give any info on the Leafs, especially manufacture date or model year?

 

[GRA]

Do they give any info on the Leafs, especially manufacture date or model year?

2012s. The full details of this testing including initial and end of test battery stats are (or were) available on AVTA's website, and have been reported here in the past. Here you go:https://avt.inl.gov/sites/default/files/pdf/vehiclebatteries/DCFC_Study_FactSheet_EOT.pdf

The general page for all BEVs tested: https://avt.inl.gov/vehicle-type/bev

 

[LeftieBiker]

2012 means that the results are only applicable to Leafs made through March of 2013. After that the degradation over time is much less, as is the heat factor.

 

[SageBrush]

I found two lab studies which may shed some light on Nissan's battery degradation and conditions for maximizing battery life:

https://avt.inl.gov/sites/default/files/pdf/vehiclebatteries/FastChargeEffects.pdf

Interesting study. A few comments:

1. The cars were NOT run down to turtle, but to 5 miles remaining on the GOM. The study estimated 10% SoC which sounds ballpark.
2. At least in the case of the DCFC arm, two charges per day so they finished that arm in around one year. Even in Phoenix, one year is not a lot of accumulated heat but some 600 DCFC events are. Perhaps one way to parse these results is to say that DFFC is at least as detrimental as Phoenix heat.

I can imagine this kind of heavy use in a commercial setting. The car is toast after one year.

This graph is really informative:

Regardless of battery age or capacity, the battery is depleted when pack voltage reaches 350 volts
Second, the dV/dAhr increases from about a SoC of 50%. That may be a nice place to estimate battery health over time and in test drives prior to purchase.

 

[LeftieBiker]

Perhaps one way to parse these results is to say that DFFC is at least as detrimental as Phoenix heat.

The available evidence suggests that QCs are only detrimental when they increase heat above some threshold in the 7-8 bar area, or occur when the pack temp is already high. QCs in cool weather may actually help the pack.