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Real World Computing

Why are laptop batteries more expensive than lawnmower batteries?

Posted on 15 Dec 2009 at 11:53

A battery-powered lawnmower brings a rant from the normally placid Paul Ockenden

I normally restrain myself from ranting in this column – I prefer to concentrate on the sunny side of mobile technology – but I'm going to make an exception thanks to a problem that’s been bugging me for a while, but came to a head this month when I bought a new lawnmower.

Now you’re thinking “Didn’t he do lawnmowers last month?”, but allow me to explain further. As I’m a certified gadget-addict, this wasn’t just any old lawnmower but a Bosch Rotak 43LI. The clue is in that two letter suffix LI – yep, a lawnmower powered by lithium-ion batteries.

If you browse the Screwfix catalogue, you’ll see there’s recently been a flood of new lithium-ion-powered garden and workshop tools – they’re rapidly taking over from NiCd and NiMH thanks to lighter weight, longer life and lack of the pernicious “memory effect”.

It’s pretty much the same battery technology used in laptops, mobile phones and MP3 players, so volume manufacture is already established.

I’m really chuffed with my new mower, but what most intrigued me were the two batteries it came with, each rated at 36V and 2,600mAh.

You might remember from school physics that when comparing battery capacities what really matters is Watt hours, which you get by multiplying ampere-hours and voltage, so these lawnmower batteries have a capacity of 93,600mWh or 93.6 watt-hours. That’s enough to light a 100W bulb for nearly an hour, or to boil two cups of water – a staggering amount of power from a battery.

If you shop around you can pick up these Bosch batteries for around £140 (although I paid £340 for the mower itself, plus a fast charger and twin batteries).

Batteries

But I digress: £140 for 93.6 watt-hours is around £1.50/Wh, and that’s where I start to get angry (and this column gets back on brief!), because I’m typing this on a Sony VAIO TT laptop for which Sony will happily charge me £220 for an extended-use battery. That 10.8V, 8,100mAh battery costs approximately £2.50/Wh, so why exactly should a laptop battery cost this much more than a lawnmower one?

Both are intended for rugged use (far more so for the mower, which is packaged in high-impact rubber); both have deep-discharge and thermal protection; both include a battery gauge; and don’t forget the mower is made by Bosch, a German company not known for positioning its products at the cheap end.

This 66% premium on laptop batteries would be annoying enough – perhaps not enough to power a full-blown rant – but I also have a few power and garden tools made by Ryobi from its excellent ONE+ range, which are also powered by lithium-ion batteries. The same calculation on their replacement batteries comes out at around £1.16/Wh, significantly below half the price of Sony’s laptop batteries.

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User comments

Rethink "stable".

How sensitive is your power drill, or lawn mower, to voltage fluctuation? Have you ever seen your drill slow down, not go as fast, when the battery gets low? How about the lawnmower, does it slowly start to slow down, or does it just cut off instantly when the battery dies?

Say your laptop needs 5V. 4.9v won't cut the mustard. That battery has to provide "stable" power in a sense completely different than your power tools do. Those power tool batteries are just batteries. They contain very little electronics to regulate power output (they do have minor electronics for charging, because LiON batteries require special charging procedures). Your laptop battery is a smarter battery, and needs to provide steady power for as long as possible. It can't brown out and expect the computer to cope with the fact.

Also, just one of Ryobi's power tool batteries weighs more than my netbook does. That's a consideration as well. Do you really want to carry around a 20 lb. notebook? Welcome back to the 90s, I guess.

By Otto42 on 15 Dec 2009

Purely Profit

Laptop batteries are not as stable as they claim. They start at 13.5V and end at 11.9V when the laptop dies.

Probably the only valid reason they give is the size - you can use lower quality batteries in a lawnmower - because you don't really want to push around your laptop.

Batteries are one of the hardest aspects of product design; combining weight, temperature resistance (you don't want a laptop battery dying if it gets cold- think lead acids) and size.

By JaredEngineer on 15 Dec 2009

Economies of Scale

Because a new battery is custom designed for each laptop, the usual economies of scale don't have time to drive the cost per unit down.

Ryobi on the other hand has a limited number of interchangeable form factors and an expectation of selling orders of magnitude of their batteries.

If you want to lower the cost of Lithium Ion batteries, it is time for an international body to designate a fixed number of form factors (Like AA, D, etc) and impose large tarrifs on companies not conforming to these defined form factors.

By anon1 on 15 Dec 2009

You think that’s bad…

Kodak KLIC-8000 li-ion batteries cost £3.46 / watt hour.

http://store.kodak.com/store/ekconsus/en_US/pd/Li-
Ion_Digital_Camera_Battery_KLIC-8000/baseProductID
.145063900/productID.145064000

http://www.google.com/search?q=29.95+dollars+%2F+(
3+volts+*+1780+milliampere+hours)+in+(GBP%2Fwatt+h
ours)

By clone53421 on 15 Dec 2009

Converting back to watt-hours

The reason batteries are listed in amp hours is because voltage varies throughout the discharge cycle. The amp-hour rating is therefore based upon the average voltage, not the nominal voltage.

By multiplying this figure again by the nominal voltage you're diminishing the impact of this adjustment. This punishes disproportionately batteries with a wider range of flux.

But the biggest issue here is that all Li-ion batteries are not created equally. They have different temperature performance, memory, etc.

Maybe for your next article you should investigate why some vodka costs $10/litre and some costs $20/litre.

By efoley on 15 Dec 2009

Usage

There is also the level of usage to consider and how this impacts onto longer term reliability.

The mower / battery combination isn't used continually (unless Chez Paul is particularly large?); typically a lawn mower would get around 50 hours usage per year.

I'm sure laptop batteries could be cheaper if you only used them once a week for an hour or so on a Sunday afternoon from March to September.

By jdb_hollybank on 15 Dec 2009

Lithium cells are complicated.

Tool batteries are most likely using either of the inherently safe chemistries, lithium iron phosphate or lithium magnesium phosphate. DeWalt uses lithium iron batteries; these have a nominal voltage of 3.2 volts and don't work with most lithium chargers. Problem is, both have lower energy per gram and energy per liter than the old-style lithium cobalt cells that are famous for blowing up in laptops. Both tool cells typically don't have trouble with heat, actually having lower internal resistance than lithium-cobalt -- lithium iron can sometimes be drained in as little as two minutes; in theory a single camera battery (123a) can provide sixty watts of power for two glorious minutes. The lithium cobalt cell has a bad habit of exploding if discharged faster than a half hour, by comparison. The sony rep was wrong on technical aspects, but right that tool packs are poorly suited for laptops, where space and mass constraints play a very big part.

As Anon1 writes,
"If you want to lower the cost of Lithium Ion batteries, it is time for an international body to designate a fixed number of form factors (Like AA, D, etc) and impose large tarrifs on companies not conforming to these defined form factors."

For the most part, this is what happens. 16340, 17670, and 18650 cells are used all over the place and are in fact standard form factors. Inside most Dell batteries, you'll find six or nine 18650 (18mm diameter, 65mm length, cylindrical) lithium cells welded together with little solder tabs. The circuit that protects them from overcharge, overdischarge, and short circuits is not standard, however, and any on-board power gauge is not standard either. Getting laptop makers to standardize their designs around standardized *packs* is probably a non-starter, and is going to unnecessarily stifle interesting laptop designs. Further making this a bad idea is the use of lithium-ion-polymer packs, which are the flat cells used in Apple's new sealed batteries, which are more resilient than traditional cells, and can be packed more efficiently, despite lower theoretical energy density.

By Ian_TechwareLabs on 15 Dec 2009

Oh hey.

I really should have used the GB Kodak site. The battery costs £29.99 in the UK…

That makes it £5.62 / watt hour.

http://shop.kodak.co.uk/store/ekconseu/en_GB/Displ
ayProductDetailsPage//productID.147410200

http://www.google.com/search?q=29.99+GBP+%2F+%283+
volts+*+1780+milliampere+hours%29+in+%28GBP%2Fwatt
+hours%29

By clone53421 on 15 Dec 2009

Any laptop can be powered by power tool batteries.

"What we really need is for someone to come up with a laptop that can be powered by power tool batteries."

Any laptop can be powered by power tool batteries.

Three things are needed:
1) Laptop Power Connector
2) Voltage Regulator (DigiKey.com should have the one you need to match the battery to the laptop for a few dollars.)
3) Battery Connector/Holder

Wire it up and presto.

cheers,
glenn

By GlennPowers on 15 Dec 2009

because Sony are ripping you off?

The extended battery on my thinkpad x60s is about 100 for a lenovo one and from about 30 for a compatible

By tim333 on 16 Dec 2009

Highly misleading story

Comparing an "if you shop around" price for a lawnmower battery against the full list price for an unusually expensive type of laptop battery?

A 58Wh battery for the latest ThinkPads costs £91.77 direct from Lenovo, or £1.58/Wh. A 95Wh battery for HP's popular dv5 series is currently £77 direct from HP, just £0.81/Wh. And let's throw in the notoriously expensive Apple - a 73Wh Macbook Pro battery direct from them is £97, which equates to £1.33/Wh.

The article is based on a rigged argument, and it serves as another example of why journos rank so poorly in trustworthiness surveys.

By pickles on 17 Dec 2009

Goodness

So many manufacturers reps . so little truth.

Since we have so many apologists for manufacturer pricing on here:

1) Please point to a cell manufacturers site where enhanced voltage stability etc are the driver for a substantial price premium on cells.

2) Please explain what portion of the initial parts costs is made up of battery and further explain why in fact the manufacturer has no possible incentive to do anything but bundle and ship the cheapest safe option that will last 3 - 12 months in service

3) Please explain the unique shapes and sizes that stop 3rd party manufacturers and packagers getting decent volumes on competing with OEM replacements. Surely if the Laptop makers were burdened by high Battery costs they would make the packs standard to get some volume economise themselves.

4) Please convince me that the replacement battery market is not just one huge cash-cow for manufacturers supported by obfuscation, warranty threats, and misleading claims.

FWIW I believe the typical manufacturing cost of a Laptop Battery is around $2 per cell plus $5 of plastic and electronics. Anyone care to show me how to pay more than this in production volumes?

How about PC-PRO starting a little campaign about the environmental impact of Laptops retired early because a new battery costs more than the depreciated value after only 2 years.

By B_Avis on 17 Dec 2009

why do they cost more? because they can get away with it.

would anyone pay £180 for a new powertool battery? unlikely, they would just buy another tool

By kingct on 20 Dec 2009

Ridgid brand power tools have a lifetime warranty on the batteries. (At least in North America)

Can't see a laptop company doing that.

Why are we charged this ?? For the same reason that the iPhone is a locked in ripoff.

Because people are stupid, and want the latest toy. :P

By RobertMc on 23 Dec 2009

In regards to my post about Ridgid power tools;

I should mention.. that means I get free replacement batteries (and other parts) as long as I own the powertool.

By RobertMc on 23 Dec 2009

Why buy a battery powered lawnmover anyway?

What I can't understand is why no one is asking the obvious questions!! Is it really that much of a pain to have a cable trailing from your lawnmower and why on earth would you pay a premium for a battery powered lawnmover, something that you use very infrequently?!?!? If you have money to burn give it me, go out on the town, treat the missus... or just burn it! And why on earth would anyone be buying a lawnmover in this weather, the grass won't even grow for months especially in this icy weather? Did you really buy one or did you just make that bit up for the story??!?! You can't trust anyone these days!

By anthonysjones on 7 Jan 2010

My Dell Laptop 90Wh batt is 20p per Watt Hour

Same capacity as your lawnmower battery for $35 delivered.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item
=270490694390

By Lestin on 17 Jan 2010

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Paul Ockenden

Paul Ockenden

Paul is a contributing editor to PC Pro specialising in smartphones, mobile broadband and all things wireless. He's technical director of a combined IT and marketing company, which works on websites and intranets for several blue-chip clients.

Read more More by Paul Ockenden

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