Post #1219: Bought a Prius Prime

Posted on August 23, 2021


That’s the plug-in Prius.  So far, my wife and I like it.  A lot.

This car is a plug-in hybrid electric vehicle (PHEV).  It’s a standard Prius gas hybrid that also functions as a fully-capable electric vehicle (EV) with limited range.

In a nutshell, this car combines good electric-vehicle performance, easy at-home recharge, no range anxiety, and all the bells and whistles that you expect to get with a modern car.

And it was cheap.  Toyota offered $5000 worth of incentives, the Federal government chipped in $4500 worth of tax credits.  Net of both, the car cost $22,000.

What’s not to like?

In Post #1150 and Post #1151, I explained that the U.S. electrical grid has been getting cleaner (lower carbon dioxide output) at a rapid rate, and that “MPGe” ratings of electric cars are a guide to energy use, not carbon footprint.  If you want some deeper background on why we’re shifting toward electric vehicles,  start there.

The back story, Part I:  Prius Lazarus

My wife and I had been casually looking for a replacement for her 2005 Prius.  After close to 200,000 miles, it was showing its age a bit. 

To be clear, we had no complaints with it.  It was a reliable and reasonably sturdy car, easy to drive in urban settings, with good utility due to the hatchback design.  We’ve maintained it, after our fashion.  E.g, the front bumper skirt is held on with duct tape, but we color-coordinated the tape with the car’s paint.

We added an aftermarket kit in 2009 that converted it into a 5 kilowatt-hour (KWH) plug-in hybrid.  With that plug-in hybrid electric vehicle (PHEV) retrofit, the car was still getting excellent gas mileage, for periods when we mostly puttered around town.  This is from a few months back, in the posts mentioned above.

That’s pretty good for old tech, but it isn’t a miracle or a trick.  The gas mileage looks good because the remainder of the transportation energy was electrical energy from the grid, charging the 5 KWH battery in our aftermarket system.  It’s not incredibly efficient, it just substitutes electricity for gasoline.

We liked that 2005 Prius so much that we did the unthinkable — we brought it back from the dead.  That is, we paid far more than the blue-book value of the car, for a major repair.  The traction battery in that 2005 Prius died at just over 175,000 miles.  (That’s the big (1.2 KWH) expensive battery used in the hybrid system.)  That was not unexpected — it had started to show signs of deterioration, and 175,000 is a typical time at which that battery would need replacement.  Rather than junk the car, we paid the dealer $4K to put in a new traction battery.  

That was about twice the Blue Book value of the car at the time.  That’s how much faith we had in that car.

Well, actually, that’s how much we loathe the process of  buying a new car.  To a large degree, we paid close to $4K to avoid having to put up with a car dealer.

(But in addition, repair was plausibly cost-effective.  Average annual depreciation on a new Prius, over its lifetime, could easily exceed $2,000 per year.  If the old car only lasted two more years, cost per year of vehicle service would be no higher than that of a new car.  The only real risk of deciding on a major repair is if it turns out to be just the first of many.  We had one other significant repair (inverter cooling pump), but so far, that string-of-expensive-repairs has failed to materialize.)


Back story, Part II:  Battery cost and gas cost.

At present, all car batteries are wear-and-tear items, just like tires and brake linings.  Electric vehicle makers don’t like to talk about that.  But batteries have a limited number of charge/discharge cycles before their degradation makes them unusable.  As battery tech improves, we may get to the point where the replacement period exceeds what would otherwise be the plausible maximum life of the car.  But in 2005, that had not quite yet happened.

This source is the most accessible that I’ve found so far regarding factors that affect EV battery deterioration.  They analyzed observations from 6000 electric vehicles.  With the most recent past generation of electric vehicles, the average rate of deterioration of battery capacity was around 2.3% per year, for the first seven years.  (With an expectation that degradation will get faster at some point in the life of the battery.)  Battery manufacturers typically chose 20% loss as the end point of battery life (although Tesla uses 30% as the standard for their battery guarantees).  Taking the 20% loss as the standard, this suggests an average life of a typical EV battery of something less than 17 years, at average driving conditions.  Obviously, YMMV.  Some models — notably the Nissan Leaf, which has no active temperature management system for the battery — have significantly shorter average lifetimes.

Everyone realizes that batteries wear out, on an intellectual level at least.  Even the best rechargeable batteries are good for a limited number of cycles.  That applies to 100+ KWH EV batteries as much as it does to 0.001 KWH rechargeable triple-A batteries.

But when it comes to big, expensive batteries, most of us would prefer to live in a fool’s paradise.  A paradise of no systematic depreciation of the cost of the battery.  And, to an extent, the world plays along.  Battery lifetimes seem to have a large random component.  Maybe we’ll get lucky.  Probably we’ll sell the car long before that big battery has died.  And so on.  And so we pretend that the battery use is “free”, and cheerfully ignore the slow but sure degradation of the battery with each charge/discharge cycle.

If you’re of the fool’s paradise persuasion, then a dead Prius traction battery comes as a great big slap in the face.  Here you were, just getting along in life, and you had the bad luck to have your traction battery die.

The ignorant make much of that high battery replacement cost.  You’ll see comments to that effect all over the internet.  But, after 175,000 miles, a dead battery isn’t exactly a surprise, if you are sane.  It’s only a surprise if you choose to live in that fool’s paradise where batteries last forever, until some day they randomly die.

Paying to replace a Prius traction battery forces you to face up to one simple fact:  Electric transport trades capital consumption cost for operating cost.  You aren’t buying gas, but you are using up your battery.  The operating-cost savings on gasoline alone overstates true long-run savings.  On average (if you ran a fleet of Priuses, say), you’d need to factor in a per-mile cost for battery wear and tear.  You need to depreciate the battery.

That raises an obvious question:  Is it worth it?  Purely in terms of dollar cost, how did the gas savings from 175,000 miles of Prius driving compare to the cost of the battery replacement?

To some degree, this next calculation I’m going to do is a fiction.  It’s fiction because only a modest share of conventional (gas) cars make it past 175,000 miles before being scrapped.  Although there are no hard numbers on this, I think it’s fair to say that scrapping a conventional car at 175,000 miles would not be unusual in the least.  And so, I could have scrapped that Prius when the battery died, with no regrets about choice of car, and no cost of battery replacement.  In other words, I’m factoring in this big repair cost for the hybrid, but I’m including nothing comparable for the comparison car, one that probably met its own car-killing repair cost long before 175,000 miles.  Blowing a head gasket, say.  (See below).

(As an aside, it turns out to be impossible to get a hard-number estimate of typically car mileage when scrapped.  Of how long cars actually last, on average, before they are junked.  You see various estimates, from various sources, but little in the way of hard data.  Based on rhetoric, 200,000 miles is something to shoot for, not something commonplace.  The only hard number I found is that of all used car sales, 1.2% were for vehicles with 200,000 miles or more (Forbes, 2018).  It’s not at all clear how that would relate to age at time of scrappage, but it suggests that 200,000 mile vehicles are either rare, or rarely sold.)

It’s also fiction because repair costs are vastly higher than the cost of constructing the car in the first place.  Accordingly, comparing the replacement cost of the battery to the value of gas savings obtained from the original battery will overstate battery costs relative to gas costs.  We’d be smarter to have figured this on the basis of the excess cost of the hybrid system, relative to a standard vehicle.  But I think this makes the point anyway.

Ignoring the quibbles in tiny type above, let me do the the crude comparison of the replacement cost of the Prius traction battery against the value of the gasoline saved over the life of the original traction battery. 

Calculation 1:  Making the jump from standard car to hybrid — a no brainer.

In this section, I compare the gas savings to battery replacement costs when we chose a Prius over a conventional car in 2005. 

Suppose we hadn’t bought a Prius back in 2005, but had bought a similarly-sized conventional car instead.  We would have avoided this $4K battery replacement bill.  But we wouldn’t have gotten 50 MPG.  On net, which would have been the greater expense?

First, the gas savings amounted to about $10,000 over 175,000 miles.  Based on EPA mileage from, the 2005 Prius got 46 MPG, while either a Camry or a Corolla of that year would have gotten 25 MPG.*  Either non-hybrid car would have used used 3200 more gallons of gasoline.  I estimated a $3.18 average cost per gallon over that time using US BLS gas price and CPI data.

* Now (2021), by contrast, a stock Prius gets 54, a non-hybrid Corolla gets 35 MPG, a non-hybrid Camry gets about 32.

The fuel cost savings from going hybrid ($10K) far exceeded the eventual $4K cost of the battery replacement.  Even at full retail dealer prices for that replacement.

To someone who’s never owned a hybrid, that full-retail at-the-dealer $4K battery replacement might sound like a shockingly large repair bill.  But it wasn’t shocking.  It wasn’t even unexpected, or somehow just a matter of bad luck.  It’s a known wear and tear item, just like buying tires from time to time.  (Arguably, I paid more for tire replacements over 175,000 miles than I paid for this battery replacement.)  It wore out just about on schedule.  And the important fact is that the cost of the repair was more than pre-paid by the savings in gasoline which that hybrid battery enabled.

Finally, this completely ignores the 31 tons of additional C02 emissions that 3200 gallons of additional gasoline would have generated.  (Less a fraction of a ton, to account for the C02 generated when creating the battery).  Not only was this cheap to run, it was easier on the environment.

Calculation 2:  Making the jump from hybrid to electric — not so easy.

Here, I’m just going to present the facts as I believe them to be.  You’d be surprised just how hard it is to track down reliable information on likely battery replacement costs and longevity.

In 2005, our decision was between hybrid and standard cars.  But now, for this section, the rational choice is between an extremely efficient hybrid (the Prius) and an even-more-efficient plug-in version of that (the Prius Prime).

The Prime adds:

  • An 8+ KWH lithium-ion (Li-ion) battery.
  • Roughly 25 mile electric range (longer in the city).
  • An efficiency of roughly 4 miles per KWH.
  • Expected battery life of 5000 full charge/discharge cycles.
  • Expected battery replacement cost of about $5500.

First, note how much cheaper this new Prius Li-ion battery is than the 2005 nickel-metal-hydride (NiMH) battery was, per KWH.  The new battery has about 7x more capacity (8+ KWH versus 1.2 KWH) but the new replacement cost is only about 35% more expensive.  That, I believe, is mostly a true reflection of the progress in battery cost and technology over the intervening decade and a half, along with a modest cost difference between the NiMH and Li-ion battery chemistries.

Source:  Arstechnica.

(N.B., As near as I can tell, Toyota set the cost of the NiHM replacement pack back when it first started producing them, and hasn’t materially changed the price since.  I’m not quire sure why, but that suggests that NiMH batteries haven’t seen the rapid cost decline that is evident for Li-ion batteries.  I could not document that.)

If you’ve been wondering why you’re seeing an explosion of electric vehicle choices, refer to the chart above.  If you wonder how Tesla can go from luxury vehicle to car-for-the-masses, ditto.  A lot of changes happen when the underlying technology gets that cheap, that quickly, and that technology accounts for a big fraction of the total cost of the vehicle.

Second, ignoring any environmental benefits, how will the operating costs of the vehicles compare, for the electrical miles driven in the Prius Prime?

Here, 5000 discharge cycles is 125,000 miles. That’s the time period I’m going to consider.  How does the cost of gas, for a standard Prius, compare to the cost of electricity plus battery repair, for the electrical miles in the Prius Prime?

Over that time period, the electrical miles will save (125,000/54 = ) ~ 2300 gallons of gas, at a cost of $7300 (based on $3.18 per gallon, as above). But those miles require (125,000/4 =) ~31,000 KWH of electricity, costing ~$3800, at a current average cost in Virginia average of 12.25 cents per KWH.  If I then add the wear-and-tear on the battery, and depreciate the battery by adding in the estimated cost of battery replacement ($5500), that comes to $9300 for the full cost of the electric miles.

In short, the electric vehicle has a slightly higher operating cost.  The operating cost of the electric miles (Prius Prime, $9300) is modestly higher than the operating cost of the high-efficiency gas-powered hybrid vehicle (Prius, $7300), once I factor in the cost of battery depreciation. 

Which, because I choose not to live in a fool’s paradise, I do.*

* Except that, if you’re following along, you’ll note that  I did not pro-rate the cost of the traction battery wear-and-tear in the standard Prius.  That’s because I have the option of buying a Prius Prime and not plugging it in.  I believe that 8+ KWH Li-ion battery should last longer than any plausible vehicle life if used solely as the traction battery for the hybrid system.  That’s a bit of a cheat, but not much.  If I’d pro-rated the cost of a standard Prius traction battery, this comparison wold be roughly break-even.

Let me emphasize that’s a slightly higher operating cost compared to a dead-cheap-to-run standard Prius.  And I cheated a bit, as described in the small type above.  You wouldn’t go wrong to say that it’s roughly break-even, even against that miserly standard.

This again ignores the carbon-footprint reduction, but those are more modest this time.  At 4 miles per KWH, the electrical miles generate about 60% less C02 than the gas miles in the Prius gas miles would, given Virginia’s generating mix.   The electrical miles would generate about 14 tons less C02 in 125,000 miles, giving me a net cost of about $150 per ton C02 avoided.  Given my other (virtually nonexistent) painless options for carbon footprint reduction, I’m happy to pay that.  (But see below on actual miles per KWH.  Actual cost per ton CO2 avoided is modestly lower due to greater-than-expected EV efficiency of the Prius Prime.)

For those who care, the production of a Prius generates more C02 than a standard vehicle owing mostly to smelting all the copper for the wirings of the motors, and the nickel for the battery.  For a standard Prius, Toyota’s own analysis showed that the “payback period” for carbon footprint was about two years.  That is, compared to a standard Toyota Corolla, the first two years of lower carbon emissions from Prius operation merely paid back the higher carbon footprint of production.  After that, the Prius produced a net reduction in carbon footprint for every year of operation.  If I can find a link to that original Toyota analysis, I’ll edit this include that.

Calculation 3:  But wait a minute …

3.1  You’re telling me that Toyota is selling a car where a $5500 component is only expected to last 125,000 miles?  That doesn’t sound like Toyota.

No, actually, I’m not.  The battery is only good for about 125,000 pure electric miles.  But if you take a long car trip in a Prius Prime, you’ll run the gas engine.  Really, any trip leg that exceeds 25 miles will be almost guaranteed to end up using the gas engine.  Those gas-powered miles don’t really count in terms of PHEV battery wear.

Even if the PHEV battery lasts for exactly 125,000 electrical miles, the car will go much further than 125,000 total miles before the PHEV battery needs to be replaced.  Unless I’m crazy enough to run it as a pure EV, and never run the gas engine.  In which case, I should have bought an EV.

My wife and I seem to be recharging that battery every other day.  At that rate, 5000 full charge/discharge cycles will take about 10,000 days.  Call it 27 years, more or less.  Given my age, and the U.S. life table, it’s a fair guess that replacing that battery is going to be somebody else’s problem.

I think, is why Toyota discusses that battery as a life-of-the-car item.  In my case, it’s likely to be a life-of-the-car-owner item, at least.

3.2  But what about tax credits?

Good point.  Toyota has been a laggard in electric vehicles, so you can still get the full Federal tax credit if you buy a plug-in Prius Prime.  That credit is $4500, given the 8 KWH battery.  That tax credit almost pays for the eventual battery replacement.  (I think that’s probably an artifact of when those tax credits were created.  They appear too generous, to me).

The upshot is that the financials on this are not nearly as grim as I painted them, thanks to the tax credit.

3.3  But what about Toyota incentives?

Here’s the real kicker.  My wife went to Connecticut to buy her Prius Prime, where the total Toyota incentives amounted to $5000.  When you figure out what she actually paid, less the federal tax credit, our new Prius Prime cost $22,000, net. 

3.4  What about all those big batteries ending up in landfills, Mr. Holier-Than-Thou Environmentalist?

As a final aside, you have to ponder the recycling aspects.  Toyota got ahead of the game, and organized centralized recycling of Prius batteries in America (per this reference).  Most manufacturers have now organized similar systems for their own batteries (per this reference).

But that approach only works with batteries recovered via their dealerships.   Toyota offers a $200 bounty on dead Prius NiMH battery packs from any source (per Edmunds, 2014).  This sets a floor on what a dead Prius NiMH battery is worth, and goes some way toward making sure they are recycled.   (Based on current metals prices, I estimate that the nickel and cobalt in the older Prius traction battery is worth about $240.  Accordingly, it will pay somebody to recycle those old Prius batteries.)

My understanding of it is that batteries not recovered via dealerships, and in particular Li-ion batteries, are a mounting problem that nobody much wants to pay attention to.  That is, either setting such batteries up for re-use as grid-based electrical storage, or for straight-up recycling.

At present, there appear to be just a handful of companies and locations in North America capable of recycling automobile Li-ion batteries at scale.  The Federal government has contracted for a centralized U.S.  Li-ion battery recycling facility (Toxco).

My understanding of it is that unlike NiMH batteries, it does not pay to recycle Li-ion batteries.  It’s cheaper to buy new materials than to pay the costs of recycling old batteries into new ones.

In other words, absent subsidy or regulation, Li-ion batteries won’t be recycled.

I look at that situation as a big problem that currently has a technical solution, but not an economic one.  Technically, battery recyclers are learning how to deal with the wide range of Li-ion chemistries.  Economically, we’re not yet willing to tax new EV/PHEV/Hybrid cars sufficiently to pay for the eventual cost of recycling their batteries, or to find some other guaranteed funding source that will then spur the private-sector creation of adequate recycling infrastructure.

In short, I don’t think there’s any technological barrier to recycling today’s Li-ion batteries at scale.  Money and political will can solve this problem.  The obvious thing to do is to tack a recycling fee onto each Li-ion battery, then set up the rules that enforce the recycling.  That hasn’t happened yet.  But I have every hope that will happen sometime in the next 27 years.

Back story, Part III:

Getting back to our story, four things prompted us to buy a Prius Prime at this time.

First, my son’s car finally died, after a prolonged illness.  He’d been driving it for months with a blown head gasket, against my advice.  He needed a new car, he’s getting a 2005 Prius with just under 200,000 miles on it, with a like-new traction battery.  (Blue Book value, given the condition of the car, is approximately zero, to within rounding error.  So that ain’t much of a gift.)

Second, the COVID-19 Delta wave was building.  We could read the writing on the wall and see that anything requiring a long face-to-face transaction was better done sooner than later.

Third, we did our homework and ran through our plausible hybrid, plug-in hybrid, and electric vehicle (EV) options.  In the end the Prius Prime hit the sweet spot, allowing us to take a step into serious electrical transport with absolutely minimum hassle.  If the battery runs out, it becomes a 54-mpg Prius.  We can charge it in a few hours using a standard 110V outlet.  And yet, it’s a full and competent EV for the first 25 miles of any trip.

You’re not going to be able to burn rubber EV mode, as you can in a Tesla.  But, get real, it’s a Prius.  If you wanted to smoke the tires on a routine basis, you wouldn’t have considered this car.

Fourth, it was cheap.  For whatever reason, in some states Toyota is really heavily discounting these.  (A tip of the hat to PriusChat for making us aware of that.)  As noted above, the total cost, net of all Toyota and Federal incentives, is $22K.

It’s hard to buy any new car that seats five for that kind of dough. Or, at least, hard to find one that a fat guy can fit into.

So far, it exceeds expectations, but it has taught me what a fogey I am.

Currently, we seem to get closer to 33 miles per charge, owing to driving EV miles gently and at low speed.  I get a kick out of using the efficiency indicators on the dash to drive with as little energy use as possible.

It has all the bells and whistles that come on a modern car.  I instantly hated all of them. 

Instead of having “a dashboard”, where some engineer thoughtfully provided you with exactly what you needed to see, you have to set up the gauges that you want, yourself.  This substitutes an untrained amateur (the car owner) for the professional engineer, and results in far too much choice.

Next, instead of sitting quietly in the garage, the car will text my wife’s phone when the battery is charged.  So now I have to wonder what it’s posted on Instagram lately, or whether it’s been hanging out in chat rooms talking to Skynet.

Third, it has “lane assist”, which boils down to constantly tugging at the wheel if the car isn’t perfectly centered in the lane.  That was the first thing to get turned off.

On the plus side, some of the controls are totally retro, and some of the safety features are welcome additions.  The AC and radio have actual, physical knobs and toggles.  I can (e.g.) turn up the AC by reaching a finger down and hitting a switch, as God intended, rather than fumbling through menus on a touch screen, a method clearly devised by the spawn of Satan.  It also has automatic braking for collision avoidance, which is a great safety feature and one I’m glad to have, even though I think it mainly benefits the short-attention-span crowd who remain glued to their cell phones while driving.


Electric cars are coming, there’s no two ways about that.  For us, the Prius Prime offered just the right combination of a gas-powered hybrid and an electric vehicle.  For some reason, Toyota and Uncle Sam seem determined to give them away.  So we bought one.  Best guess, with our driving patterns, the majority of miles will be electric miles, but we’re not limited to electric-only use.

For us, it’s so far, so good.

On the one hand, the Prius Prime isn’t a full EV, but we’re moving in that direction.

On the other hand, half a pack a day is still smoking.  We’re still going to burn some gasoline.  Even in a fuel-efficient Prius, here in Virginia, those gasoline miles generate far more C02 than electric miles will (Post #1150).

But as far as I can tell, the constraint on shifting our transportation miles to electricity is no longer about the technology.  Battery technology today is better and vastly cheaper than it was a decade ago.  For most people buying EVs new today, they’re never going to have to face that battery-replacement decision.  (Though you would hope that somebody would, down the road, rather than just scrap the car.)

Instead, I think the biggest constraint on the shift to lower-carbon electric transport is demand.  It’s in the willingness of the buyer to move from liquid fuels to electricity.  It’s in the hassle factors over the range.  It’s in the need add wiring to the home to provide adequately short recharge times (or in the lack of a place to recharge routinely at all).  And it’s in the fear of that big repair bill once the battery pack wears out.

There are maybe two points to this posting.

One is that there are options that get you most of the way to electric transport, but skip all the hassle. Assuming your thinking isn’t cemented in last century’s technology, buy a PHEV.  No range anxiety, no need to add a separate charging circuit to your house.  No nothing.  Everything is optional.  Plug the car in when you can, use it in EV mode when you can.  That’s it.

The other is that the fear of battery replacement cost is overblown, particularly when you put that in the context of operating cost savings.  It’s overblown because Li-ion batteries are getting better and cheaper.  And it’s overblown because even at today’s full retail, your savings on gas costs over the life of the battery should more than pay for the battery replacement.  From a lifetime cost-of-ownership perspective, all of that C02 emissions reduction from electrical miles is more-or-less free.  Even when I use the gas-miserly Prius as my standard, if I should live that long, I’ll come out very close to break-even on the battery replacement cost for this Prius Prime, versus the cost savings from electricity over gasoline.

I admire people who’ve gone full EV, particularly the early adopters.  I’m guessing that if we ever buy another car, it’ll be an EV.  But for now, PHEV provides a way for my family to drive electrical miles with none of the shortcomings of purely electrical transportation.  So that’s the direction we took.