For our river trip next month we will want to keep some electronics charged up for photos and lighting. We wont have cell signal so the phone batteries will save a lot of power in airplane mode. I am also bringing a lot of batteries (8) for the GoPro so that I can take a few time-lapses and get fun shots of the trip.
To keep phones and watches charged we will want to bring a few portable batteries and a solar panel. When at camp we will be sure to have the panels out and charging battery packs and/or devices. Since we will be in a jungle I want to be conservative about how much solar charging is going to happen. Better to have too many batteries than too little.
The question is how much battery backup do we need for an 8 day voyage?
The back of an envelope calculation for portable chargers is to divide the charger’s capacity (mAh) by the device’s mAh. If a charger is 10000mHa and the device is 2942mAh then you should get 10000/2942 = 3.4 charges before the charger is depleted.
With batteries I like to round down as it is better to have too much than too little. So in this case I would say that the device should be able to be recharged 3 times.
For this trip we are taking two 20000mAh packs and one 10000mAh pack. That gives us 50000mAh to charge two iPhone XR’s (2942mAh each) and two Apple Watches (~285mAh each) for 8 days. 50000/6500 = 7.7 charges to full for all devices combined. That gives us almost a charge a day, which we should not need since the phones will be in airplane mode.
To safeguard ourselves, and ensure much epic footage is shot, we are taking a 28W solar panel system. We will be able to use this before and after each day of rafting and keep either devices, chargers, or both topped up as much as possible. Hopefully this means we won’t ever deplete one of the battery chargers completely. Which will avoid us having to stress about battery management too much and instead on enjoying the trip.