It wasn’t that long ago that our agency had thousands of people with laptops who travelled often (2007). We used to give them two batteries, a home charger and a car charger. You could get almost four hours on a full battery and that was not running a ton of software and no WiFi or wireless. Seemed common if you travelled to have more than one battery. Now it seems like you just want one of those battery backups to bring with for times when you don’t have a plug nearby.