Africa's "smart phones" (whatever that means) are usually a feature-phone with a web browser. Much less capable than a smartphone

Turn off wifi and 3G/4G see how long your smartphone battery lasts. Oh I did this recently with an old phone, it lasts around 4 days as well (and that's with an old battery)

Also a lot of apps abuse smartphone processing updating how many times per minute

But screens and processing power still cost a lot of energy