Why are laptop batteries more expensive than lawnmower batteries?

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).

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.