Source: Amazon
They say there’s no saint like a reformed sinner.
And, I swear this is going to be my last post on electric vehicle batteries.
I just need some closure. Because I’m still fairly ticked about this entire episode.
For a year and a half, I adopted the obvious but destructive habit of plugging in my wife’s car as soon as I returned from a trip. That way, it would always be fully charged when we wanted to use it next. Easy-peasy.
As it turns out, discussed in the just-prior post:
- charging it to 100% shortens battery life
- charging it to 100% and letting it sit around shortens battery life a lot
(And when I say 100%, I mean to the highest charge level the car will allow. I realize that Toyota built in a roughly 15% buffer, so that the literal state of charge is around 85% when it says the battery is full. All car makers do that. And some people say that provides all the protection you need. But I don’t. More importantly, the National Renewable Energy Lab (NREL) doesn’t. The battery life simulation below assumes a 10% buffer, so SOCmax is 90% true state-of-charge. You can take their chart, relabel the lines by adding 5% to each label, and that ought to be a pretty good estimate of what you should expect with a Prius Prime. And, based on that chart, you would expect to shorten the life of the battery substantially if you always charge to (what the car tells you is) 100%.)
Source: Optimizing Battery Usage and Management for Long Life, Kandler Smith, Ying Shi, Eric Wood, Ahmad Pesaran, Transportation and Hydrogen Systems Center, National Renewable Energy Laboratory, Golden, Colorado,
Advanced Automotive Battery Conference Detroit, Michigan June 16, 2016 Annotations in red are mine.
If I had only:
- Read the fine print in Toyota’s highly-touted 10 year/150,000 mile battery warranty to realize that there is zero warranty for loss of range.
- Scrutinized page 143 of my 800-page owner’s manual, and realized the significance of this sentence:
- “Use the charging schedule function as much as possible in order to fully charge the hybrid battery (traction battery) immediately before starting off.”
- And had the wit to realize that while Toyota said “Use the charging schedule function” they actually meant “don’t let the battery sit around fully charged.”
If I had put all that together — for this new car that was functioning and driving perfectly, getting better-than-EPA gas and electrical mileage — I would never have made that mistake.
Instead, I probably would have figured out that the $10 countdown timer, pictured above, would have prevented almost all the abuse I was heaping onto that (plausibly) $5000 battery.
The only new thing to report is that the cheap timer picture above seems able to handle the 12-amp charging current just fine. And I’ve changed my bad habits. My new policy is to give the car an hour of charging, if the charge is low when I get back from a trip. It’s a simple as plugging it in and pushing a button. But otherwise, I’ll put the car on to charge, for a few hours, when I make the coffee in the morning, so it spends the greatest amount of time a some moderate state of charge.
That cheap, simple change is all it took to eliminate a potentially battery-killing bad habit.
My sole remaining concern is that some EV charging systems only “balance the battery pack” or equalize the voltage across all cells at the very end of the charge cycle. If that’s true for the Prius Prime, I’m going to want to do an occasional 100% charge in order to get that done from time to time.
An unexpected bonus is that I can take advantage of the “charging curve”. The closer you get to 100% charged, the slower the charging gets. A rough rule-of-thumb is that the last 25% of range takes half the total charging time. And so, while the car takes more than five hours for a full charge, it only takes an hour to go from ~40% to ~80% charged.
Anyway, no saint like a reformed sinner. I hope I can be the person that I want to be. As pictured below.
Source: Electrek.co. Annotations in red are mine.
