Although I have a spare battery (or two) with me when in the field, purely as a comfort blanket, I'm yet to get close to using one.Seriously!!!!!!
A number of friends who are keen photographers have EM10's and EM5's and none of them have spare batteries and they all go out and take photo's on day trips and very rarely run into any battery issues and never enough to drive them to buy a spare.
The average owner of most cameras doesn't need or want a spare battery, i don't have a spare for my TG5 or PM2.
a friend doing there own product photography only just bought a spare for their em1mk2 and only because they currently have a lot of products to do.....