If you're thinking about buying a portable cell phone charger: google the mAh of your phone. Look at the mAh of the charger you are considering. If you do the math, it will tell you how many times the charger can charge up a completely dead battery. Fuel Rod is probably less than once.
If you have a bad back, also look at the weight of the charger. It might weigh more than your phone. That adds weight to your park bag.
Pay attention to the USB port on the charger. The charger will come with a cable that you plug into your phone or tablet adapter, then plug the adapter into an electrical outlet to charge the charger. But the part of the cable that plugs into the adapter might be USB-A. Also when you plug your phone into the charger, the charger's port might be USB-A. But newest iphones are Lightning to USB-C. Do you have an adapter and cable which are USB-A, if that's what charger uses?
Anker and Mophie are reputable brands which can be found at Target,
Walmart,
Best Buy and
Amazon.
I know some people (not me!) are proud of their plan to limit their cell phone use on vacation. But I enjoy taking photos, and I use my phone as my camera.
We're expecting up to a foot of snow tonight and may have power outages. I'm going to go plug in my portable charger in case we lose power.
Edited the next morning to add: we didn't lose power on my block, but 37,000 people in the area did. If we had lost power, at least I would know that I could keep my phone charged!