Battery Life and Sitting at 100% Charge

I've got a battery life concern raised in this post from another thread (and see that post for good info on battery life):

Urk! I'm retired and don't drive every day. So my PIP will sit fully charged for three or four days a week, assuming I plug it in and set the timer each time I get home.

Does that mean my battery life will be dramatically shortened?

First, the Prius does not charge to actual 100%. All "battery percents" the customer can see are renormalization of an operating window from 21% to 82% (approx numbers, don't know if formal numbers are known for pip). So "0" is really 21 and "100%" is really 82%SOC. Toyota, GM/ Ford are not letting you get to a full 100% charge to protect the battery, the Leaf and Roaderster allow true 100%.. which is potentially risky if you then let it sit in the heat. Again, when you see 100% charged, you are at say 82%.. and that's not a problem.

Not much need for you to worry. You seem to be in the bay area, so no excess temps there. So even the lack of TMS is not a problem for you.

Enjoy your PiP, and don't worry about it. Toyota has you covered.

Edit: note however that Toyota does recommend delaying charging until just before you use it.. so if you can follow that advice it will generally be better for you battery.. but you'll have to balance no charge when you need it vs the minor risk of slightly increase decay rate. The post I had in another thread (2015 PIP to will have a significantly longer range | Page 4 | PriusChat) shows its not near as bad at mild temps, but then what is the risk. Personally I do charge to about 8am (also best to charge a cool battery and, in winter, drive a warm one.)

I had the same concern. I also work at a college on the top of a hill. I charge at work and drive down hill for 5 miles. Thought for sure I was going to burn out my battery, but the car allows another 2-3% charge after I unplug before the engine turns on to absorb the energy.

I also plug in at night (5 am end time) and the car sometimes sits until about 9 or 10 am before I drive it. No worries. If you let it sit for a few weeks at 100% soc, then I'd worry.

I also started thinking about when I do short trips around town and have a battery at about 3/4, then plug back in because I have a larger distance to drive in an hour or so. I've heard that plugging back in to top off was bad... anyone else want to chime in on this?

True topping off (to true 100%SOC) is bad. But a PiP only "tops" off to 82 or so true SOC, so its probably not a problem at all.

and yet, the owners manual recommends against letting it sit with a 'full charge'. i'm sure they mean when possible.

Hmm my bad then, I've not read the PiP manual in detail. I guess Toyota is playing it safe and it could be significant in high-temp areas. (Probably not in the Bay area, though maybe in San Jose..)

I guess that is because the PiP does not have thermal management. GM explicitly says to keep the Volt plugged in which means fully charged, but it can use TMS to keep the battery in ideal range of temps. But on reflection I guess I can see it as the Volt will actually use battery power to keep it in the right temp range until the battery is about 70% usable SOC and at that point it stop cooling unless plugged in.

Toyota recommends "storing" the PiP with NO EV range, long term. In other words drive it until its in HV mode, then power down the car and leave it.. That puts the pack somewhere near %18-22 SOC.

For daily driving, they recommend having the charging finish shortly before driving the vehicle, but it's not critical, it's designed to keep the car from having a higher SOC for an extended amount of time, but even when the PiP shows "full", the pack is NOT at %100 SOC, more like %82-85. This is to maximize pack life before the capacity starts to drop, you don't have to follow it exactly, it's just a recommendation. A high state of charge, combined with high ambient temperatures are what lead to pack degradation.

It's thought Toyota is using roughly %70 of the SOC range, with it's 4.4KW pack, that leaves us with about 3KW of usable energy.

Actually, I presume it's just because it's safer and a bit better for battery life to have it sitting with less charge.

this is one reason why i have been thinking about L2 charging, it allows a bit more flexibilty when you need to go somewhere unexpectedly rather than leaving the car charged all the time or leaving it uncharged and not having enough warning to give it a full charge with L1.

I am considering the EVSE upgrade to 240

just FYI - according to my scangauge, the ICE kicks in at 85% SOC to start bleeding charge off the battery. generally the SOC is around 84% after a full charge. the ICE starts up again at 23% SOC when the car goes back into HV mode. the SOC has to rise to about 28-29% before the car will show that it's possible to re-enter EV mode.

i have taken to plugging in for an hour and a half in case i need to go somewhere unexpectedly. then, plugging in again for the remainder if i don't use it before leaving for work. does anyone think leaving it half charged for 4-5 hours a day will be detrimental to battery life?

Nope. Because "full charge" is only about %85 SOC.
If you leave it like that in the Mohave desert for an extended time, it might cause slight degradation.
In Boston, no problem. Toyota recommends leaving the pack in HV only if the car is going to be left unused for an extended time (months)

Heat and High SOC are what cause pack degradation...

Only if you move to TX or AZ or someplace that gets above 90 nearly half the time you leave it partially charged.
And even then it might reduce your battery life to 120,000 miles rather than 150000... (just making up the milage numbers.. but at 40-50% charge is near ideal for some li-on chemistry.

When I first bought the car, I plugged it home as soon as I got home from work. Then, I drove the car to work, using about half of the EV range. I'd use the remainder up at lunch or on the drive home. So I was keeping the battery in a fully or partly charged state for up to 18 hours a day.

But now, when I get home from work, I press the dash button to set a 6:00 AM Charge Stop time. I drive to work in all EV mode, so the battery depletes first thing. So now, the battery is in a charged state an hour each day, and it's discharged the other 23 hours... more or less.

thanks guys! nice to know a little more about li-on.

As a physician whenever I return home I plug my prius plug in into a level II charger. My profession involves on call responsibility to a hospital which means I could have to leave my home and be prepared to leave my home at any time night or day. It is mandatory that I keep the battery charged, in order to use the car as an electric vehicle. I do hope Toyota took this application into consideration when offering this vehicle for use here in America.

you'll be fine. there will be some extra long term degradation, but that's the cost of doing business, right?

With the 8 year warranty, any degradation on battery performance will be covered.

Unfortunately I don't think it will cover that.
Page 11 of the plug in prius warrenty guide says

I think it would cover it if it completely stopped working (e.g. cell shorts), but if the EV range is reduced significantly that would not be covered. As I recall, the major EV/PHEV players, only the GM Volt has any warranty on capacity/range. probably because they went with the Thermal Management System to protect it.