Post #1776: Gas versus electric mowing, Part 6: Why I’m not buying a battery-powered mower

Weird, eh?  I’m happy to rely on a (mostly) battery-powered car.  But I don’t want a battery-powered lawn mower. Even though I used a plug-in electric mower for years.

I swore off battery-driven power tools years ago.  So, for me, it’s not as if this is some new stance.

In this post, I explain why.  Why I’m not going for a battery-powered mower.  And why I no longer buy any power tools that run on batteries.

Let me emphasize that my decision isn’t due to ignorance.  If anything, it’s because I’ve had too much experience with big lithium-ion batteries.


A few things about lithium-ion batteries.

Practically speaking, your sole option for a walk-behind battery-powered mower is lithium-ion batteries.  There have been some riding lawn mowers powered by lead-acid batteries.  But I don’t think there’s anything on the market today not powered by lithium-ion batteries.

Point 1:  Maybe you can recycle them.

Almost no lithium-ion batteries are recycled in the U.S.

I’m acutely aware of this because a) I bought a 200-pound lithium-ion add-on battery pack for my wife’s Prius in 2008, and b) recycling of those big lithium-ion batteries has been just around the corner for the past 15 years.  I think my most recent post on that was Post #1715.

Still don’t believe that lithium-ion is rarely recycled? Here’s a handful of relatively recent references.

That last reference is particularly illuminating.  Read down to the part where the Federal government is still at the point of offering cash prizes for anybody who can figure out how to do it cost-effectively.  Its not merely that lithium-ion batteries aren’t recycled, it’s really that there’s not even one good, standardized, agreed-upon process for doing it, let alone doing it cost-effectively.

Post #1712 has the details, but the reason for the lack of recycling is obvious.  It costs money.  Reportedly, Tesla currently pays $4/pound to recycle is lithium-ion batteries.  Even with that, the cost of post-recycled lithium is higher than that of virgin lithium, making it an uneconomic source for production of new batteries.

Still, some stores — around here, notably Home Depot — have boxes where you can drop off old batteries weighing under 11 pounds.  That should cover most lawn tool batteries.

That’s free to you because Home Depot covers the cost of processing those via call2recycle.  This is an organization whose funding comes from battery- and battery-powered device manufacturers, or from organizations willing to pay to recycle those batteries.   For example, their board of directors has representatives from Panasonic, Sony, Energizer, and Duracell, among others, based on their 2021 annual report.

You can see examples of their retail pricing on this page.  It looks like they charge about $2.50 a pound to take boxes of mixed rechargeable batteries off your hands.  So Home Depot is paying on-order-of $12 to allow you to dispose of a 5-pound lithium-ion lawn mower battery.

What happens after that is a bit unclear to me.  For sure, the value of the materials recovered appears trivial.  Here’s their 2021 Annual Report, showing revenue sources.  Less than five percent of their revenues comes from the materials recovered from those batteries.

Source:  call2recycle 2021 annual report.

They do not break out their collection and recycling costs separately.  Combined, those account for the bulk of their costs.

At any rate, they are clearly at least paying to have those batteries disposed of properly.  What fraction of the materials actually ends up in new products — is actually recycled — is not possible to determine from their annual report.

Interestingly enough, when I look up their lithium-battery recycling partners, the only U.S. partner appears to be a 2021 startup.  Which again seems to emphasize just how iffy lithium battery recycling remains, at this time.

Fifteen years.  For fifteen years, I’ve been living with a 200 pound LiFePO battery pack.   And for fifteen years, large-scale lithium-ion battery recycling has been just around the corner.  Which is right where it is today.

Point 2:  Batteries trade lower fuel cost for higher capital consumption cost.

Which is a fancy way of saying, if you want to keep using the tool, you have to keep buying batteries.

We replaced the nickel-metal-hydride traction battery in my wife’s (now son’s) 2005 Prius somewhere around 178,000 miles.  Doing the math, the cost of that new battery ate up roughly half of the total lifetime savings in gasoline costs, from driving that efficient hybrid compared to a similarly-sized non-hybrid 2005 vehicle.

But it’s not just the dollar cost.  It takes quite a bit of energy to manufacture batteries, something that contributes to the multi-year “payback period” of a Prius relative to a non-hybrid automobile.  For the first couple of years that you drive a hybrid, from a carbon-footprint standpoint, all you are doing with your lower fuel use is paying back the higher energy cost of the vehicle’s manufacturing.

In particular, worst-case (made-in-China, meaning, made using coal-fired electricity), large-format lithium ion batteries result in the release of roughly 200 kilograms of C02 per KWH of battery capacity (calculated from this MIT reference, 16 metric tons per 80 KWH battery pack).

And so, creating a typical lawn-mower battery — 0.3 KW (72 volt, 4 amp-hour)  would result in (200 KG/KW x 0.3 KW * 2.2 lbs/KG = ) 132 pounds of C02 released into the atmosphere.

I use 2 gallons of gas a year to mow my lawn.  That generates about 40 pounds C02 per year.  The upshot is that even if my electricity were carbon-free, I’d spend the first three years of battery-powered lawn mowing merely paying back that initial 132-pounds-of-C02 debt, for the manufacture of that disposable battery.

That’s not a huge surprise, to those of us who have been using big battery-powered objects.  It was an estimated two year payback period for a 2005-era Prius, where the battery and motors didn’t really power the entire car.  So, a three-year payback period for a small tool that’s entirely battery-powered?  To me, based on my experience with the Prius, that seems entirely plausible.

As for the energy cost of the rest of it, I’ll just point to the high energy cost of smelting copper.  Electric motors require quite a bit of that, which is another reason hybrids require more manufacturing energy than non-hybrid cars.  Plausibly, depending on expected lifespan, there may be no manufacturing energy savings in the non-disposable portions of the devices.

For an extremely-long-lived battery, such as one used in a car, that payback period usually isn’t much of a consideration.  You’re saving a ton of fuel, and the battery will typically last well over a decade.  Overall, it’s a winner, even if you fully acknowledge the energy cost of producing the battery.

Here’s the kicker:  How long do those lawn-mower batteries last?  Every website I visit seems to give the same answer of three-to-five years.  So they might last long enough to pay back that initial carbon-footprint debt.

The upshot is that a lithium-ion powered lawn mower is a fine way to reduce local air pollution.  It may not be such a winner from the standpoint of reducing your carbon footprint.  And since global warming/carbon footprint is my main concern, I’m not hugely attracted to those devices from an environmental standpoint.

In addition, knowing what I now know about lithium-ion batteries, I’d bet on the lower end of that three-to-five-year range.  My wife’s new Prius — a Prius Prime — arguably contains a $12,000 lithium battery pack.  With no warranty to speak of.  So I got kind of serious about not trashing that.  And that’s when I learned the rules for lithium-ion batteries.  See Post #1703.

The rules, in brief:  Lithium-ion batteries don’t like heat.  They don’t like to be fast-charged.  They don’t like rapid rates of discharge, either.  And they really don’t like being worked from fully charged to fully dead.  They much prefer shallow charge-discharge cycles.

And yet, every manufacturer seems intent on using them in all the wrong ways, in mowers.  These will see highest use in the heat of summer, and typically be stored in a non-climate-controlled space.  Everybody seems to charge their lawn-mower batteries at a “1 C” rate of charge or higher — from dead to fully charged in one hour.  (Presumably, that’s to all ow you to swap batteries continuously and mow very large lawns.)  I’m pretty sure manufacturers allow the full capacity of the battery to be used, unlike cars that reserve the top and bottom 10 to 15 percent as a buffer against over– and under-charging.  (That’s why a 72-volt battery pack can be advertised as 80 volts, because once you’ve absolutely fully charged it, that’s what it’ll read, despite the fact that charging it to that degree is bad for battery life.)

Point 3:  If you love buying name-brand inkjet cartridges, you’ll enjoy purchasing batteries for your lawn mower.

Here, I’ll just refer to the highest-rated 21″ walk-behind battery powered mower on Amazon.  This is the Greenworks Pro 80V 21″ model, with 4.0 Ah battery.

On Amazon, the complete mower, with battery and charger, is $425.  But the replacement 4.0 Ah battery, by itself, costs almost $300.

In short, your cost of the replacement battery is 70% of the total cost of the functioning lawn mower.  And, as with power tools of all sort, manufacturers go way out of their way to make sure that only their batteries will fit their tools.

This, more than anything else, is why I swore off battery-powered shop tools.  It’s the monopoly-exploitation aspect of the battery replacement.  Once you’ve bought into a particular manufacturer’s line, they’ve got you.  And as far as I was ever able to tell, generic batteries manufactured to fit those tools are all completely dreadful.  So if you want a battery that works, for that name-brand tool, you pay that name-brand price.

Once I bought my third $45 battery pack, for my $60 drill, I did eventually figure out that a battery-powered drill is an expensive way to make holes in stuff.   That drill eventually got to the point where battery packs were no longer available.  (Which, if you own one long enough, will happen.)   At that point, it too became just another particle in our great national solid waste stream.  And was replaced by a corded drill.

Point 4:  Caginess about power.

This is more of an irritation than a point of substance.  But take any battery-powered lawn mower on the market, and try to find out the peak power of the electric motor, expressed either as kilowatts or as horsepower.  Nobody will tell you that basic information.

At some level, the average power output is just basic physics.  The mower above has a 72-volt, 4 amp-hour battery, and claims to be able to run for an hour on that.  That should be sufficient to cut my half-acre lawn.

But do the math.  How much energy is at your disposal, for that hour of mowing?  Well, 72 volts x 4 amps = ~300 watts of average instantaneous output.  Or, over the course of an hour, you have 0.3 KWH of power available to you, to accomplish your hour of mowing.  For sure, your peak power output will be much higher than that.  But if that battery is going to last an hour, it can’t put out more than an average of 300 watts, over that hour.

One horsepower is about 750 watts.  So the average available power output is less than half a horsepower, if you’re going to get your hour of mowing out of that battery.  Again, peak output will clearly be many multiples of that.  But that’s what you have, to get through your lawn, on average, over the course of an hour.

In my case, there are parts of the lawn, at times of the year, that nearly stall the Honda 3.3 KW gas engine that runs my mower.   I would love to know that some prospective battery-powered mower has a peak power output that meets or exceeds that 3.3 KW instantaneous power output.

But here, I bring up the last thing I know about lithium-ion batteries.  If that battery could, in fact, produce 3.3 KW of instantaneous power, it would be discharging at more than a “10 C” rate.  (That is, at that rate, the battery would be dead in less than one-tenth of an hour.)  Discharges at rates like that are unambiguously bad for battery life, for traditional cylindrical-design lithium-ion cells.  So even if it could match the peak power of my current mower, I’m not sure I’d want it to.

In other words, just as was true for my old corded Black-and-Decker, I’m pretty sure that the mower will get through my lawn.  But I’m also pretty sure that I’m going to have to “baby” it when the going gets really tough. 

But short of buying one and using it, there’s no way for me to tell, because manufacturers do not disclose peak power output of these mowers.  And so, how well will some battery-powered mower cut through stands of uber-thick Zoysia grass?

Instead of providing me with the concrete information that would allow me to judge that, manufactures require that I take a guess.  And when I see something like that, I assume it’s because their product would appear in an unfavorable light, if that information were disclosed.

Let me put it this way:  If those battery-powered lawn mowers had peak power that exceeded that of a typical gas mower, you can bet that manufacturers would crow about it.  So I think the absolute silence regarding peak power output tells me more-or-less all I need to know.

Point 5:  Summary

For the time being, I’ve decided to continue using a gas-powered lawn mower.  It’s a modern overhead-valve design, and (best guess, see prior post) mowing produces as much smog-forming pollution per hour as driving a mid-2010s-era sedan for an hour.  That’s clearly a downside, compared to battery-powered mowing, but not an extreme one.  For good measure, I’ve tossing my antiquated gas can in an effort to keep my gas-powered mowing as clean as possible.

My main environmental concern is global warming, and it’s not clear that a battery-powered mower offers much advantage there, compared to gas.  That’s due to the carbon-intensive nature of lithium-ion battery production and the relatively short expected lifetime of those batteries in fairly harsh use conditions.

Otherwise, not switching to battery-powered mowing is mostly a question of avoiding annoyances.  No mower maker will bother to tell me peak power.  So I suspect that will be lacking.  Each mower maker uses proprietary batteries.  So I expect to pay an outrageous amount for them.

And the whole lithium-ion battery-recycling thing is one big question mark.  Yes, you can drop your dead lawn mower batteries off at Home Depot, and Home Depot will cover the cost of getting them recycled, to some degree.  The degree to which the material in these batteries is actually re-used is far from clear.

So that’s it.  I saw a compelling reason and significant gains from switching car transportation to electricity.  There, at issue was a considerable amount of gasoline burned per year, batteries with an extremely long projected life-span, and some guarantee of responsible end-of-life recycling via Toyota.  Maybe. And the driving experience is better under electricity than with gas.  For mowing the lawn, by contrast, at issue is just two gallons of gas a year, there’s no clear benefit in terms of carbon footprint, and I’m betting that it’s harder to mow with a battery-powered mower than with a modern gas mower.

So this is one area where I’m not going to electrify the task.

Post #1775: Gas versus electric mowing, Part 5: Finally, a sensible estimate

To cut to the chase:  I use a 21″ push mower with a modern Honda overhead-valve engine.  Starting from EPA data on emissions for engines of that type, I calculated two simple rules of thumb, for the pollution generated by my lawn mowing.

If the standard of comparison is the typical car on the road — call it a mid-2010s full-sized sedan — then gas lawn mowers are 100 times dirtier than gas cars, per horsepower.  And an hour of mowing generates about as much pollution as an hour of driving.

That’s just the mower.  That doesn’t include emissions from your gas can, as outlined in the just-prior post.

Also see Post #1776, explaining why, despite this level of pollution, I’m not going to switch to an electric mower any time soon.  This, even though I drive an electric car (Post #1924, et seq.) Continue reading Post #1775: Gas versus electric mowing, Part 5: Finally, a sensible estimate

Post #1722: Gas versus electric lawn mowing, part 2: The information you seek is not available.

 

Husqvarna versus Hummvee.  The one on the left is the true environmental bad guy?  Really?  Who says so?  And how do they know?

This post is the second in a series tracking down the origins of this generic statement:

  • One hour of mowing your lawn using some gas-powered lawn device
  • produces as much something-something-something
  • as 200 or 300 or 350 miles of driving something.

The information you requested is unavailable.

A good overview of this issue can be found on The Straight Dope.  Note how old that is — that posting dates to 2010.  Clearly, many variants on this one-mower-hour-equals-300-miles theme already existed at that time.  That posting specifically notes that all of the information behind that claim was made obsolete in 2012, when the EPA issued new standards for pollution from small engines.

And yet, we still see that exact same language today.  It was one hour equals 300 miles (say) 20 years ago.  And it’s the same today.  Despite the 2011/2012 EPA regulations limiting small engine pollution (Source:  EPA).  And despite two decades of changes in passenger vehicle technology and mix of vehicle types.

I get my first clue about the loosey-goosiness of this mower-versus-car statement from the California Air Resources Board (CARB), which currently says (emphasis mine):

Today, operating a commercial lawn mower for one hour emits as much smog-forming pollution as driving a new light-duty passenger car about 300 miles

Based on that critical word — commercial — maybe the commonly-cited one-hour-equals-300-miles statement has little to do with my 21″ Husqvarna mower with its Honda GVC-160 engine.  It was based on … something else.

And as I dig deeper, I’m beginning to understand why I couldn’t find any details on what these lawn-mower-versus-car statements actually mean.  After some hours of internet search, I can find authorities such as CARB that make those statements.  But I can find absolutely nothing on the details behind those statements.

In short, I know what CARB said, but I still know nothing.  I have no idea what CARB means by:

  • “a commercial lawn mower”, or
  • “a new light-duty passenger car”, or
  • “smog-forming pollution”.

As far as I can tell, CARB provides no details whatsoever.  Or, at least, none that I can find on their website.  Do they mean operating the equipment in a typical use-case, or do they mean running it full throttle, flat-out?  Do they mean a new piece of equipment, or the average mower currently in use.  How big is a commercial mower?  Does “passenger car” include SUVs or not?  Did they use a specific passenger car, such as a Prius?

And I still don’t know how to scale it down to my actual, as-used 21″ lawn mower.

Even worse, after looking into the regulations, I may never know how much pollution that mower emits.  That’s because U.S. regulations appear to be stated in terms of maximum limits, when the engine is run through a pre-defined duty cycle.   As far as I have been able to tell, nobody publishes the actual as-measured data on actual engine use.


Can you derive that statement from the regulations?

Now things get really nuts.  Even if I can’t find data on actual emissions, I ought to be able to find information on emissions limits for small engines and cars, and compare them. 

And I can do that.  The only problem is, if I do that accurately, with modern emissions limits, that makes small engines appear vastly worse than the one-hour-equals-300-mile meme suggests.

Let me start with my lawn mower, with a Honda GCV-160 engine, displacement of 160 CC or 9.8 cubic inches, rated for 4.4 horsepower or 3.3 KW.  All of that is per Honda.

Next, the EPA standard for “Class I” small portable engines is 10 grams of NOx and exhaust hydrocarbons per engine KWH per hour.  So, for the Honda engine rated at 3.3 KW, the EPA would appear to allow 33 gram per hour, combined NOx and exhaust hydrocarbons, under its mandated duty-cycle testing.

But the EPA standard for cars (shown here) works out to new-fleet average of just 0.03 grams of NOx and exhaust hydrocarbons per mile, for all passenger vehicles.

When I put those together, the exact statement appears to be that for one hour of running my Honda-powered lawn mower, the EPA allows that mower to release as much N0x and unburned hydrocarbons as (33/0.03 = ) 1100 miles of driving, by the average new gasoline-powered passenger vehicle.

I think I understand why I get such an extreme answer.  I used the modern (Tier 3) emissions standards for cars.  Those only went into place around 2017 or so.  Whereas these statements about mowers-versus-cars originated much earlier.   If I track down the Tier 2 standards for cars, and use the cleanest “bin”, the standard calls for no more than 0.125 grams NOx and unburned hydrocarbons per mile.  For that standard, the maximum allowable NOx and unburned hydrocarbon emissions from one hour of mowing equal the allowable emissions for (33/.125 =) ~250 miles of driving a typical passenger car at the maximum allowable Tier 2 emissions.

So it appears plausible that the one-hour-equals-300-miles statements derive from comparing maximum allowable levels of smog-producing exhaust emissions.  And that if anyone bothered to update those old statements to the current (Tier 3) car standards, they could make an even more extreme statement.

But.  But those are the upper limits on what is allowed.  They aren’t the actual emissions.

And none of that squares with the current CARB statement cited above.  For CARB to make that one-hour-equals-300-miles, they had to specify a commercial (presumably, large) lawn mower.

So I now think I understand how you could come up with that statement.  But I’m still not quite sure whether that statement reflects the real-world outputs of those pollutants.

Still, it remains plausible that a small lawn mower engine really is that “dirty”, by modern car standards.  The EPA estimates that modern vehicles produce about 2% of the smog-forming pollutants that (say) 1960s-era vehicles did.  And, basically, lawn mowers are still back in the 1960s in terms of pollution controls.  Catalytic converters, sealed fuel systems, exhaust-gas regeneration — all of those pollution controls are standard on cars, and unheard-of on lawn mowers.

In any case, I’m going to keep digging.  Somewhere, somebody should be able to show actual measurements of emissions of a modern lawn mower, in a form comparable to emissions measured for a modern car.

Post #1721: Gas versus electric lawn mowing, part 1: The conundrum

 

Preface:  I was an early adopter of electric lawn mowing.  Early, in this case, being somewhere around 1995, well before battery-powered electric mowers existed.  But after a couple of burnt-out mowers and many trashed extension cords, I gave up and bought an efficient gas walk-behind mower. 

That was circa 2015, and I have not looked back.  Until now.  This is the first of a series of posts looking at gas versus electric lawn mowing.

Part 1:  The conundrum

I keep reading ever-more-outlandish statements about just how much pollution gas lawn mowers generate.  Depending on which source you read, you will come across this generic format:

  • One hour of mowing your lawn using some gas-powered lawn device
  • produces as much something-something-something
  • as 200 or 300 or 350 miles of driving something.

Weirdly enough, it’s always one hour.  Everything else varies from source to source.  In addition, I am not the only person to have noticed that these car-versus-mower statements are all over the map.  This has gotten to the point where the EPA apparently doesn’t support statements like this any more (reference).

I’m sure there’s some truth in there, somewhere, but that has the look of a standard advocacy statement.  Typically, if you take one of those apart, you’ll find that somebody has purposefully created a worst-possible-case-vs-best-possible-case contrast.  Statements like that are crafted to convince rather than to inform.  And that’s done with forethought,  in pursuit of some presumed policy or economic goal.

Worse, as variants of that get tossed around, further and further from the actual research, they start to take on urban legend aspects.

Let’s play “spot the loony”.  Consider this statement, from an otherwise reputable source, Family Handyman magazine:

One hour of running a gas mower emits as much carbon dioxide as driving a car 300 miles, ...

That’s obviously a mistake.  Carbon dioxide (C02) emissions are directly proportional to the amount of gasoline burned.  Each gallon of gas generates about 20 pounds of C02 (Source:  EPA).  The average new (2021) U.S. passenger vehicle, including electric and plug-in cars, gets less than 25 MPG or equivalent (Source:  EPA).  Taken literally, the statement above says that a lawn mower burns (300/25 =) 12 gallons of gas per hour?

Must be one hell of a lawn mower.  Big agricultural combines (as above) can easily have that level of fuel consumption.  But not your typical 21-inch 3.5 HP Briggs and Stratton lawn mower.

My wife confidently informs me that we burn two gallons of gasoline per year, cutting our grass.  She’s confident because a) she mows the lawn, and b) she hates putting the gas can in her car.  So she’s sure she does that once per season.   This, on a half-acre suburban plot, less the footprint of house, driveway, and landscaping.

By contrast, for cars, in the U.S., we burn an average of about 650 gallons of gasoline per licensed driver per year (Source).  For me and my wife, if we were average, we’d be burning 1300 gallons of gasoline per year, in our car. (We aren’t — we drive a Prius Prime and arguably use about 40 gallons of gas per year in that.)

Plus two more gallons, for the lawn mower.

So there’s the conundrum.  Where does this gas-lawn-mower-as-environmental-horror-story come from, given how little fuel the typical suburbanite consumes for lawn mowing, compared to driving?

For sure, the carbon footprint of our gas lawn mower is rounding error in the context of total household fossil fuel use.  Not because small gas engines are any great shakes.  Simply because the fuel used to mow the lawn is negligible.

For perspective, using Virginia’s power generation mix (0.65 lbs C02 per KWH), two gallons of gasoline generates as much C02 as 60 kilowatt-hours, or roughly 160 watt-hours per day.   Based on these typical wattages, the gas lawn mower has the same carbon footprint as the following daily use of these home appliances:

In short, for my primary environmental concern — global warming — mowing the lawn just doesn’t matter.  Or, it matters less than many other common activities of daily living, such as washing dishes or watching TV.

But I still would like to know the full story here,  Given the small amount of gasoline consumed, how closely does whatever-it-is that is the underlying research actually apply to my situation?  Should I consider early retirement for my gas lawn mower, in favor of battery-powered?  Should I plan on buying a battery-powered mower if and when my current one dies?

I already know some of the answers.

Briefly:   First, the horror story is about smog (not carbon footprint).  Second, it focuses on major small-engine consumers of gasoline.  The total environmental impact appears to have been estimated based on consumption of 3 billion gallons of gasoline annually, for lawn and garden equipment.  With lawns surrounding roughly 100 million U.S. households, that works out to about 30 gallons of gas, per lawn, per year.  Or about 15 times the rate at which my mower uses gas.

The upshot is that I’m not deeply concerned about this.  But I would like to know more.  The rest of the posts in this series will dig a little deeper into this, including (if possible) finding the original EPA research that has spawned this class of gas-lawn-mower-bad advocacy statements.

More to come.  It’s a nice day.  I’m going to go work in the yard now.