Backpacking Joules

The aim of this project is to provide data that assists in choosing what USB battery pack to carry when wilderness backpacking for trips spanning 5 or more days. It was found the Nitecore NB10000 has a capacity sufficient for multiple days in the backcountry and the best capacity-to-weight ratio of the options tested. 

The content below is for entertainment or informational purposes only. So don’t come crying to me when your headlamp dies and you didn't see the skunk that wandered into your campsite after dark!

Wilderness Backpacking is a fantastic way to disconnect and challenge oneself. Other than sources of light, it may seem ironic that one would want to figure out the optimal amount of electronics to bring into the backcountry. While smartphones are the portal to what one might be trying to disconnect from, they are convenient as they can be used both as a camera and a GPS-enabled navigation tool. While emergency beacons are only intended for emergency use, they enable communication with the outside world. Ultimately, it’s up to each individual to decide how much disconnecting the individual wants, and to manage how the devices are used. 

Typical electronic devices brought into the backcountry are a headlamp, smartphone, and emergency communications device. Traditional headlamps use alkaline batteries, but headlamps with internal Li-ion batteries that charge using a standard USB interface exist. Smartphones are convenient as they bundle a camera, GPS, maps, interface with the emergency beacon, and charge from a standard USB interface. Emergency beacons enable communications where cell reception is limited as they communicate over a satellite network and charge from a standard USB interface. Choosing devices that all charge from the same interface means one can reduce the number of backup batteries brought. No more AA batteries for one device, AAA for another, D cells for a third, and a USB battery pack for your phone. 

This test aims to provide information on selecting an appropriate size battery pack for the end user by measuring how much energy is required to fully charge a smartphone (iPhone 6s Plus), an emergency beacon (Garmin Inreach), and a headlamp (Nitecore NU25). The charging capacity of three USB battery packs will then be measured to estimate how many times a battery pack can charge several devices. 

Each user will have different equipment and use cases. Some may use the smartphone more than others, some the emergency beacon, and others the headlamp. Raw numbers and an example case will be given so readers can estimate their own scenarios. 

Test Instruments

Voltage Source BK Precision 9182 Programmable Power Supply

Programmable Load BK Precision 8600 Programmable Load

Multimeter Agilent 34401A 6.5 Digit Multimeter

Devices Under Test

USB Battery Pack Nitecore NB1000 5.3oz 10k mAh USB battery pack. 

USB Battery Pack Anker PowerCore 10000 6.3oz 10k mAh USB battery pack. 

USB Battery Pack Anker PowerCore+ 26800 20.8oz 26.8k mAh USB battery pack. 

Smart Phone iPhone 6S Plus Smartphone used for pictures and backcountry navigation. 

Emergency Beacon Garmin Inreach Emergency communication beacon with mapping & GPS. 

Headlamp Nitecore NU25 Lightweight rechargeable LED Headlamp. 

Setup the test equipment as indicated in the diagrams. Connect a test laptop to control the programmable voltage or current source and to monitor the ammeter and volt meter. It’s important to pay attention to the configuration of the ammeter and voltmeter to avoid the resistance of the ammeter influencing the test result.

Measuring the Charging Requirements for the Cell Phone, Emergency Beacon, and Headlamp. 

1. For the Cell Phone, Emergency Beacon, and Headlamp as the DUT: 

2. Fully discharge the DUT. 

3. Set up the circuit as indicated in the “Charge Monitoring Setup” diagram with the DUT. 

4. With the voltage source output turned off, set the source to 5V/1.0A. 

5. Start logging the voltmeter and ammeter measurements at 0.2s intervals. 

6. Turn on the output of the voltage source. 

7. If turning on power causes the DUT to turn on, turn the DUT off ASAP. 

8. Continue logging until 600s after the load current drops below 10mA. 

9. Turn off the voltage source output. 

10. Fully discharge the DUT. 

11. Repeat steps 1-10 five times for each DUT. 

12. Calculate the watt-hour capacity for each DUT by summing the product of current * voltage * timestep of each sample for each run of the DUT. Average over the number of runs for each DUT. This will calculate the number of watt-hours required to fully charge the Cell Phone, Emergency Beacon, and Headlamp.

Measuring the Discharge Capacity of each USB Battery Pack: 

1. Setup the circuit as indicated in the “Discharge Monitoring Setup” diagram with the Nitecore 10k as the DUT. 

2. With the load turned off, set the load to a constant current of 500mA. 

3. Start logging the voltmeter and ammeter measurements at 0.2s intervals. 

4. Turn on the programmable load. 

5. Continue logging data until 30 seconds after the Nitecore shuts off. 

6. Turn off the load. 

7. Fully charge the battery pack and repeat steps 1-6 five times. 

8. Calculate the watt-hour capacity by summing the product of current * voltage * timestep of each sample  for each run. Average over the number of runs. This will calculate the number of watt-hours the battery pack can source.

Nitecore NB1000 35.3 Wh

Anker PowerCore 10000 32.3 Wh

Anker 26800 81.3 Wh

Iphone 6S+ 16.1 Wh

Garmin Inreach 12.3 Wh

Nitecore Headlamp 3.7Wh

It’s important to remember that the results of this test are for informational purposes to aid in decision making and not intended to be used as a specification for the devices listed. The results are specific to each item as no statistical sampling of products was done. Factors that will influence the number of watt-hours a battery pack can supply or a product needs to fully charge are in part dependent on the age of the cell, charge cycle count, variation within manufacturing tolerances, environmental conditions, and various other conditions. 

The difference in results of the Nitecore NB10000 and Anker PowerCore 10000 was surprising. However the Nitecore uses a 3.85V Li-ion cell, whereas the Anker uses a 3.6V cell, meaning it’s expected for the Nitecore NB10000 to have about 7% more capacity than the Anker PowerCore 10000. The Anker PowerCore+ 26800 had the highest capacity, slightly over 2.3 times the capacity of the Nitecore but at 3.9 times the weight. Given the three choices, for the application of Wilderness backpacking, the Nitecore NB10000 makes the most sense. If more capacity is needed, multiple Nitecore NB10000 packs can be carried and weigh less than the larger Anker PowerCore+ 26800. 

Focusing on the Nitecore NB1000, it was calculated that the battery pack could fully recharge the iPhone 6s Plus just shy of 2.2 times (2.2 times less 120mWh), the Garmin Inreach 2.8 times (with 860mWh remaining), or the Nitecore headlamp 9.4 times (with 238mWh remaining). 

Considering the purpose of having devices that all charge from the same standard means the battery pack can be shared for recharging all devices, it was calculated that the Nitecore could give the iPhone 1.4 charges, the Garmin 0.8 charges, and the Headlamp 0.7 charges with 309mWh leftover. Of course, there are other valid combinations of charge multiples, these are shared because they are in line with my experience and typical use case. 

It’s important to remember the purpose of a portable battery pack is to recharge devices, meaning the trip starts with a fully charged device. When discussing the results with non-technical friends who enjoy wilderness backpacking, I found myself having to reiterate that one gets n number of charges out of the battery pack means that the device has a total of n+1 discharges as it starts fully charged.