Is there a cellphone charger that will keep my phone on while I travel, without needing daily access to power outlets? ?

Yes, you can get powerpacks. None of them will keep your phone charged forever. I usually travel with 3 charged ones. However, I have to point out that most planes now have outlets at the seats to plug your phone into, and you can charge your phone while you drive. What kind of travel are you talking about? If you're camping out in the wild, take some powerpacks. 

What Miguel said.  Get a decent capacity power bank.  They are relatively inexpensive, like $30 for a decent one. Just pay attention to how the power bank is charged.  Some have a USB port for charging, I much prefer the ones that charge by a normal power outlet. 

.... You don't know what a "powerbank" is? 😂