Tips to Extend Battery Life of Your EV

[mbepic]

I come across this article that may be helpful for us all.

http://www.plugincars.com/eight-tips-extend-battery-life-your-electric-car-107938.html

Just this past week-end, I had to take an extended trip with my 1 month old Bolt EV and I turned off 'Hilltop Reserve' when doing the advance charge. On the way back home, with only 100 miles range left, I found that I had to stop at two different locations for a free charge in order to get back home, about 150 miles. Anyways, when I arrived home, there was about 20 miles left on the battery and the DIC showed 'Charge Battery Soon', etc.

My question is: has Chevy allowed any buffer at the bottom of the battery to provide for longevity or if I had of used my 20miles to nothing, does that really mean 'nothing' literally. I know my Chevy Volt allowed for about 20% 'buffer' and would never allow battery to be empty; how has the BOLT EV been engineered in this context?

 

[sparkyps]

GM manages the battery to prevent over-discharge and balance the desire for range against charge/discharge cycles.

So no a range of 0 miles does not mean the battery is fully discharged.

 

[mbepic]

GM manages the battery to prevent over-discharge and balance the desire for range against charge/discharge cycles.

So no a range of 0 miles does not mean the battery is fully discharged.

Do you know of anything from GM tech that explains the 'battery management' specifically for the BOLT?

 

[sparkyps]

GM manages the battery to prevent over-discharge and balance the desire for range against charge/discharge cycles.

So no a range of 0 miles does not mean the battery is fully discharged.

Do you know of anything from GM tech that explains the 'battery management' specifically for the BOLT?

If you are asking for the algorithms they use to manage the battery, compute range, decide what voltages to charge to and what voltage to discharge to, no.

But in general terms GM and their battery manufacturer understand that there is a range of voltages to maintain the battery within to give it the desired longevity (charge/discharge cycles) and range and that determines where "empty" and "full" are even though they could obtain longer range by charging it to a higher voltage and discharging it to a lower voltage or longer life but shorter range by making the high and low voltages closer together.

In my personal opinion there is no reason for Bolt owners to spend any time worrying about charging it to "full" or not discharging it to as close to zero as they feel comfortable driving it and I expect that GM has no interest in their car owners fretting about it either.

 

[mbepic]

GM manages the battery to prevent over-discharge and balance the desire for range against charge/discharge cycles.

So no a range of 0 miles does not mean the battery is fully discharged.

Do you know of anything from GM tech that explains the 'battery management' specifically for the BOLT?

If you are asking for the algorithms they use to manage the battery, compute range, decide what voltages to charge to and what voltage to discharge to, no.

But in general terms GM and their battery manufacturer understand that there is a range of voltages to maintain the battery within to give it the desired longevity (charge/discharge cycles) and range and that determines where "empty" and "full" are even though they could obtain longer range by charging it to a higher voltage and discharging it to a lower voltage or longer life but shorter range by making the high and low voltages closer together.

In my personal opinion there is no reason for Bolt owners to spend any time worrying about charging it to "full" or not discharging it to as close to zero as they feel comfortable driving it and I expect that GM has no interest in their car owners fretting about it either.

Relative to your last sentence, I think owners should know that there is a 'buffer' at the top and at the bottom so they don't fret about charging with 'hilltop reserve' off all the time or should they turn it on to preserve the battery. Same with discharging the battery. I'm not fretting about it but owners should know something as simple as that (GM's battery management). I haven't found any Chevy Bolt documentation that would explain that simple information.

 

[JeffN]

All evidence points towards the Bolt EV having relatively limited "anti-brick" buffering at the low end and similarly limited amounts at the top end -- something like 4-5% each on top and bottom. Anti-brick in the sense that if the battery really goes to zero it can be permanently damaged. This could happen because the state of charge estimate was slightly incorrect leaving the battery to be run down too close to zero or the car might be left in a near empty state for a long time and slowly self-discharge to zero. The bottom anti-bricking buffer guards against that. It also protects the battery from the worst stress of being overly empty (or full at the top end) which increases permanent battery degradation over time. Lithium ion batteries charged over about 95% full age much faster just from siting around (called calendar aging) especially when they are also hot.

So, really full or really empty is not great for battery longevity but it allows nearly full use of the battery for long range when needed.

Having the battery "empty" or "full" means either the cathode or anode is fully stuffed with Lithium ions while the other side of the battery is full of teeny tiny holes where those ions used to be. When the graphite in the anode of the battery is packed full, for example, it causes the anode to swell slightly and literally puts mechanical stress on it. There is a thin layer of molecules that grows on the surface of the anode called an SEI (Solid Electrolyte Interphase layer) that contains Lithium ions and chemistry from the liquid or gelled electrolyte in the cell that forms a thin barrier.

This anode swelling can cause small cracks in that SEI layer which then permanently grows over the crack to fill the gap and in that process locks up more Lithium ions in the SEI. This additional SEI layer then leaves less Lithium ions to be exchanged during the charge/discharge cycle thus allowing less energy to be stored in the battery. The graphite swelling can also cause parts of the graphite to fracture in ways that prevents Lithium ions from being stored.

This is all a real thing which you can find discussion of in many battery research papers. These negative battery life effects are greatly reduced by leaving a little buffer at the top and bottom of the charge range of the battery but even with ~5% buffer there is some greater degradation than if the buffer was 10%. Or 15%. Or 20%... Battery makers have gotten better by tweaking electrolyte chemicals and graphite particle composition to reduce this effect but it still exists to some degree. Battery thermal management helps a lot. Using Hilltop Reserve probably helps somewhat for daily charging in the long run.

For my own Bolt, I use Hilltop Reserve and try to avoid discharging the battery below the usable 10% level but I'm fine with turning off Hilltop mode if I need maximum range during a road trip. Since GM leaves it off by default it probably means that daily "100%" charging (really like 95%) does not hurt calendar aging too much due to the Bolt's thermal management. I've been told that in hot climates the car will actively cool a fully charged battery even when the car is turned off and unplugged for this reason.

At the end of the day, being nice to your battery will likely extend its life a bit and therefore may be worthwhile but it's not worth wringing your hands and obsessing.

 

[mbepic]

JeffN, your reply was a bit more technical than I was looking for and I do understand the degradation factor when allowing completely discharging or completely charging a Lithium battery on a regular basis.

In conclusion, I will take your word for it that the GM or LG engineers have set a 5-10% unused buffer at the top (aside from Hilltop Res.) and bottom of the battery. I will just simply drive and charge my BOLT without sweaty palms.

Thanks,

 

[joe]

I believe tip 8 would be true for a Leaf, but is it necessarily true for a Bolt? If the DCQC rate is around 1C for the 60 kWh pack and the battery is being thermally managed, does it really reduce the life that much?

 

[mbepic]

I believe tip 8 would be true for a Leaf, but is it necessarily true for a Bolt? If the DCQC rate is around 1C for the 60 kWh pack and the battery is being thermally managed, does it really reduce the life that much?

Yes, but need to know what actually occurs during the 'fast charge' cycle that tends to degrade battery cells; also makes me wonder about the Tesla fast charging? I would try to avoid it if you don't really need it. Back in 2012 when I test drove a new Leaf, the sales person was adamant that you only used the DC charge periodically, if needed.