I had spare batteries when using feature phones. And most of the time I'd want to use one the spare would be dead, because: 1. the main battery is dead because

I had spare batteries when using feature phones. And most of the time I'd want to use one the spare would be dead, because: 1. the main battery is dead because I didn't think about charging it. The chances I would have remembered charging the spare were abysmal as well. 2. I also need a spare charger for the spare battery. Or I'd need to swap it in the phone when I have access to an outlet, and it would take twice the time to charge the main battery and the spare. Again, time and preparation. All in all, an extension to the phone is clunky, but still the best trade-off if I needed it.