SOC% drops fast below 40%

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specialgreen

Well-known member
Joined
Mar 26, 2017
Messages
246
Location
Minnesota
My 30kwh 2017 Leaf S had the battery module reprogrammed last summer to fix the "incorrect" low readings of SOH. I noticed that the GOM reads higher on a full battery, and SOH% drop seems slightly slower.

However, once last fall, I thought I'd noticed the SOH dropping like a stone when the battery is more depleted. I experienced that today.

I had SOC of 43% (on the dash, not leafspy), with GOM 41; then drove 21 miles on the freeway (55 to 65 mph). The SOC dropped to 8%, a drop of 35% over 21 miles, for a drop of 1.67% per mile driven. I've seen SOC% drop by 1.0 to 1.25% per mile driven, but pretty confident that 1.67% is unusual.

I am suspicious that my SOC is not dropping linearly from 100 down to zero. It seems as though SOG% decline speeds up as SOC drops.

**EDITED to call it SOC, not SOH **
 
+1 on checking with LeafSpy, this doesn't sound normal. I also have a 2017 S with the BMS update and noticed the same initial increase in SOH after the reprogramming. But SOC vs mileage is very consistent for me now and I've run it down to roughly 15% SOC several times. Even at at sustained 65 mph that usage sounds high unless the heat was cranked, the roads were snowy, there was a strong headwind, etc.
 
OP says that the observation is sporadic. That argues against it being a battery programming or cell problem. Just a bad hair day.
 
Given the recent temps in Minnesota, I would say dropping that fast with freeway driving is probably expected...Probably had the heat on too, correct?
 
I drove it down to "---" again today. This time, the SOC decline seemed linear. Both times, I shut off all environmentals (big round button), headlights and seat heaters, then drove home.

3 days ago, I took freeway half-way (at 52mph), then switched to surface streets to conserve energy. I did not make it, and had to pull into a L2 charger 5 miles from home. This time, I drove all 20 miles home on the freeway at about 51mph, with SOC declining from 33%. It showed as 6% after I plugged-in (1.35% per mile decline). I get about 1 mile per % in summer at 55mph. I have snow tires, and there's a bit of snow on the road. For 51mph with no heat, 1.35% per mile seemed a bit high, but not as bad as 3 days ago.

I think temps were -6F 3 days ago and -10F today, so... colder today.

3 days ago, it seemed like it started dropping faster once I exited the freeway: slower driving, but stoplights, etc. (this is with heater/fan off).
 
You have a new car, with a 30 KWH battery.

I don't understand why you are doing experiments of bringing your battery down to zero.....

Firstly, It is bad for your battery. Secondly, how can you possibly EXPECT that any part of the battery discharge curve be LINEAR??? And if it isn't, who cares? Nothing in the world is linear.

Your car sounds like it works fine, stop looking for a "hair on an egg"....
 
I use 1% per mile as my yardstick as well and it's close in the winter. I get a bit higher in the summer but I'm in CO where the air is thin.

I've noticed an efficiency drop when the roads are just wet, even more when they're snowy. I wouldn't be surprised at 1.35% / mile with a little snow on the roads. Try coasting on dry pavement vs snow covered pavement. The difference is significant.
 
powersurge said:
You have a new car, with a 30 KWH battery.

I don't understand why you are doing experiments of bringing your battery down to zero.....

Firstly, It is bad for your battery. Secondly, how can you possibly EXPECT that any part of the battery discharge curve be LINEAR??? And if it isn't, who cares? Nothing in the world is linear.

Your car sounds like it works fine, stop looking for a "hair on an egg"....

State of Charge is a computed value, and SHOULD be fairly linear by design.

My experience with this problem (rapid decline at the low-end) tended to happen if I had not allowed the pack to balance itself adequately. This was an easier problem to run into back in the days of programmed 80% charge level, but some people may still encounter this if they make an effort to not fully charge and/or regularly disconnect the EVSE before the balancing phase is complete. It also could be due to one or more weak cells so I'd make sure to give a few full charges (including a few hours after for balancing), and then check the behavior again and keep tabs on the cell voltages near the bottom of SOC.
 
powersurge said:
I don't understand why you are doing experiments of bringing your battery down to zero.....

Work. Shuttling things between work sites. I L2 charge to 100% overnight. At the end of the day, I may get down to (say) 25%. I have to decide (just for example):
- do I drive 15 miles home (reaching home with 10% or less) and charge overnight
- or drive 5 miles to an L2 and sit there for 30 minutes (cutting into my dinner time) just to add 10% so that I get home with 20%

If I know that I can get home safely without hitting VLBW, I've been just driving home and plugging in immediately. Maybe that's worse for the car than I thought.

The day the SOC seemed to drop faster, I took city streets home (assuming that would maximize my range). The SOC seemed to drop by more than 1% per mile. A few days later, something similar happened (I had to make a decision to go home, or go sit at an L2 first), and I took the freeway home at a below-traffic speed, which seemed to consume the expected 1% SOC per mile.

Heater might explain it (if using 3kw-5kw, then even 35 mph driving on city streets could use more energy than 55mph driving on the freeway, because it takes twice as long).

Anyways, I have not noticed SOC dropping faster than 1% per mile since that. Maybe it was a fluke due to bad cell balancing.
 
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