Excellent point by Bob. You need to look at your latitude, time of year and weather. All big factors.
For example my tent trailer's solar system can recharge my batteries in a couple hours after a lot of night use... under ideal conditions. But I have a large battery bank (250 amp hours) and a 250 watt solar array. That way if it rains for a week I do not have to be concerned about power (no sun), I have plenty of battery reserve and when the sun comes out can recharge it fairly quickly.
Now if you have a nominal system, when backpacking, that can only replenish what you use under optimum conditions and no method for reserve capacity, you are going to end up with some dead batteries.
I have a GoalZero panel and battery pack but have not really played with it much (it was a gift). If I were to bring electric devices backpacking I would probably be better off with spare batteries and on a long trip like the PCT would recharge at stops in town. Unfortunately the most popular phone, the iPhone, has an internal non-field replaceable battery... a big negative for that device.