Why are laptop batteries more expensive than lawnmower laptop batteries?

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. 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). That 10.8V, 8,100mAh battery costs approximately ?2.50/Wh, so why exactly should a laptop batteries cost this much more than a lawnmower one? 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.