"Full" battery levels dropping daily

[gpsman]

I recommend charging to 100% once a month as a Bolt Owner for 16 months and 16,000 miles.

I monitor this thing very closely tabulating every watt-hour.

While I have no proof regarding the “health” of the battery, I have proof the range gauge, the “guess-o-meter” gets worse and worse the longer you avoid 100%.

The car only “knows” you have 60 kWh at 100%.
(Or conversely, knows you are at 0 kWh at 0%.)

When operating in the middle, it is always a guess.

I estimate up to 0.5% error on the guess-o-meter for each day of driving without a full charge.

Yes, once I went 30 days in a row of partial charges and partial discharges.

When I finally let it go to 100%, it took 15% more power to reach 100% than it should have. Meaning my estimated range was 15% higher than actual. No good if I were attempting a long trip that day.

ALWAYS charge to 100% before attemping a trip that will use 75% or more of your battery charge.

It's generally excepted that you should charge it up full (100%) and run it down low (not 0 but low) once and a while, not to make a habit of it but like every couple months or a few times a year? To make sure everything is getting a chance to balance properly.

Honest questions - Who recommends that? And what do we know about how Chevy balances the cells in the battery?

We know about Leaf batteries because many people have done deep dive studies, watching the cells balance, etc. Have there been studies into the Bolt's battery? Has GM or LG said anything official? Or are we just extrapolating from other vehicles' behavior?

We do know some things about lithium batteries, which applies to some extent to all chemistry variations. For example, sitting at a very high or very low SoC is stressful and causes degradation over time. Also shallower charges are less stressful than deeper charges. For example, charging from 25-75% twice is much easier on the battery than charging from 0-100% once.

 

[GetOffYourGas]

All very interesting. So should I charge it to full once before a long trip, or is just-in-time charging good enough? Specifically, here's my situation. What do you recommend?

I charge to 90% (full, but with hilltop reserve) once a week, on Friday. That gets me through the weekend usually. Next weekend I am going on a 250-mile trip, which is all highway. I plan on charging once along the way, but want to have a good estimate from the car. I really don't want to get stuck. I intended to charge to 100% on Friday, right before I leave. Will that calibrate the computer enough, or should I try to do a full charge-discharge cycle before then?

 

[DucRider]

All very interesting. So should I charge it to full once before a long trip, or is just-in-time charging good enough? Specifically, here's my situation. What do you recommend?

I charge to 90% (full, but with hilltop reserve) once a week, on Friday. That gets me through the weekend usually. Next weekend I am going on a 250-mile trip, which is all highway. I plan on charging once along the way, but want to have a good estimate from the car. I really don't want to get stuck. I intended to charge to 100% on Friday, right before I leave. Will that calibrate the computer enough, or should I try to do a full charge-discharge cycle before then?

If you drive full day of freeway driving on Friday before you charge for your trip, the computer will best be able to estimate the distance you will get on a full day of freeway driving on Saturday :idea: Best estimate will come if the temperature, wind, vehicle speed, vehicle load, altitude change, etc. are also the same.

But seriously, if you just watch your mi/kWh you'll have a pretty good handle on available range, and the computer will adjust long before you burn thru an entire charge.

 

[GetOffYourGas]

I should have been more clear. I'm concerned about the BMS knowing exactly how much charge remains in the battery, not even resisting driving efficiency.

 

[IMAdolt]

I should have been more clear. I'm concerned about the BMS knowing exactly how much charge remains in the battery, not even resisting driving efficiency.

No one aside from perhaps the engineers that designed the system seem to know exactly what's going on with the chemistry and the BMS. The kind of cycling you're talking about, charging hill top most the time and once and a while doing a full charge and also depleting the battery somewhere well bellow half from time to time then you're doing about all you can realistically do by habit and I wouldn't pay special attention to it beyond that.

We're all just guessing anyway.

 

[gpsman]

I do not think a realistically full discharge cycle is needed before your long trip.

Just take it off hilltop reserve and do a “complete” charge the night before. Let it go until it says “complete” in the app. Which is slightly more than “full”.

You get a message of “Full” at about 98%.
The last 2% always takes a random, unpredictable amount of time. But that is when the important cell balancing and range recalibration takes place. You won’t find that in the manual, but it is based on my countless observations.

If the car predicts “complete by 5am” allow enough time for it to stay on the plug for an extra hour past that mark. I’ve seen it take 45 minutes longer to complete that estimated when the calibration is way off. Once in a while it gets done 15 minutes sooner. But usually ( 8 out of 10? ) it takes longer than predicted. It will of course take longer than predicted also if any heating or cooling takes place.

All very interesting. So should I charge it to full once before a long trip, or is just-in-time charging good enough? Specifically, here's my situation. What do you recommend?

I charge to 90% (full, but with hilltop reserve) once a week, on Friday. That gets me through the weekend usually. Next weekend I am going on a 250-mile trip, which is all highway. I plan on charging once along the way, but want to have a good estimate from the car. I really don't want to get stuck. I intended to charge to 100% on Friday, right before I leave. Will that calibrate the computer enough, or should I try to do a full charge-discharge cycle before then?