I see a lot of smart phones that you can't use for more than a few hours.

1. Long time to hit 100%. That issue is on most batteries today. Think of it like a bus. The bus is easy to fill to 90% but as that last space is filled it takes longer as people (electrons in the case of the battery) to find a place to be.

2. Smart phones at first were not made to be used for that many hours. This is what we used PCs for but that has changed and people now use the phone over the PC. This is why there's quite the market for external batteries for smart phones and more.