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==Batteries and Electrical Power Supply==
The optimal power supply on a long-distance hike is a subject with opposing opinions and a wide range of products that promise the solution. I try to analyse this subject with Engineering methods based on actual measurements and calculations to challenge my own habits and no fall victim to false advertisements and myths.
Before I dive into detail a brief explanation of the used terms and units :
*'''Voltage''': Unit: Volt (V). If comparing different batteries and devices you should know the nominal Voltage. Non-rechargeable Alkaline and Lithium batteries provide approximately 1.5 V. Rechargeable NiMH batteries have a slightly lower voltage of about 1.2 V. Rechargeable Lithium-Ion batteries supply 3.7 V. All USB devises work with 5 V. This applies to USB power consumers and USB power banks with Lithium-Ion batteries. These power banks have electronics that steps up the voltage to 5 V. For more information see Table 113: See the battery and power bank specifications section.*'''Electrical Current''': Unit: Ampere (A) or Milliampere (mA). 1000 mA equals 1 A.*'''Electrical Power Consumption''': The commonly used unit for small electrical devices is Watt (W) or Milliwatt (mW). 1000 mW equals 1 W. For DC consumers the power consumption can be calculated by multiplying the supply voltage with the required electrical current. In example a GPS device that is powered with two AA NiMH batteries (2 x 1.25 V) and draws a current of 50 mA has a power consumption of 125 mW (or 0.125 W). Manufacturers sometimes provide the power consumption in Ampere (A) or Milliampere (mA) what is scientifically incorrect but not an issue if the voltage is known. The conversion between current (A) and power (W) is made by multiplying the current with the voltage.*'''Electrical Energy Consumption''': The technical correct unit is Watthour (Wh). Note the difference between power and energy: power (W) is the rate of consumption while energy (Wh) is the accumulated consumption. So the energy consumption is the summed-up power consumption over a given time span. If you want to compare power and energy with hiking than power is like the speed and energy is like the distance covered.
Stored Electrical Energy: The technical correct unit is Watthour (Wh) but battery manufacturers often use Milliamperehour (mAh) to indicate the capacity of a battery. This is scientifically incorrect but when comparing batteries of the same type this works. But when comparing different battery types the unit mAh is misguiding. A Lithium-Ion battery with a capacity of 1000 mAh stores more energy than a 2000 mAh NiMH battery because the Voltage of a Lithium-Ion battery is higher. A Lithium-Ion battery with a 1000 mAh capacity contains roughly 3.7 Wh while a 2000 mAh NiMH battery contains only 2.4 Wh. Note that USB power banks are not rated based on the output voltage but based on the capacity of the internal Lithium-Ion battery.
*'''Specific Stored Energy: ''' The technical correct unit is Watthour per Kilogramm (Wh/kg). This number tells how much electrical energy is stored in relation to the weight of the battery or power pack. You can calculate the specific stored energy of a battery by dividing the stored electrical energy (Wh) by the weight of the battery (kg). As a hiker you obviously want this number to be high, to have as much as possible energy packed into as little as possible weight. But the battery chemistry puts physical limits to this. Understanding this helps to identify obviously false advertisements. I.e. if someone offers an AA NiMH battery with a capacity of 3500 mAh he scams. See the table about battery and power bank specifications for more detailed information.*'''Energy Transfer Efficiency''': When charging an electrical device i.e. with a power bank some losses occur. A part of the energy will no end up in the charged device i.e. the smartphone battery but get lost in form of heat while charging. The common unit for efficiency is Percent. An energy transfer efficiency of 75% means that only ¾ of the stored electrical energy ends up in the charged battery. When charging a device from the grit in a town you do not need to worry about this, but when charging a device on the trail with a power pack this becomes relevant.
Effective Stored Electrical Energy: Unit: Watthour (Wh). This is the amount of the electrical energy of a power bank that ends up the in the charged device when considering the losses of the energy transfer process.
*'''Generated Electrical Power''': Unit: Watt (W). Today a wide range of outdoor gear promises a free recharge of your electrical consumers on the trail. Most common are solar panels but also water and wind turbines pushed on the market. The most weird gear I have seen is a stoves that promise to produce electrical energy using the thermoelectric effect. The power might be free but always comes with a weight penalty. Therefore the following is of importance:*''Specific Power Generation: Unit'': Watt per Kilogram (W/kg). This is the actual archived power output divided by the weight of the device. This number shows the difference between a gadget that just appears cool and an actual useful piece of gear.
===Electrical Energy Consumption===
The actual electrical energy consumption during a long-distance hike depends on the electronic consumers and their use.
A Garmin handheld GPS device has a energy consumption of 1.5 Wh to 2.5 Wh per day if the previously recommended power saving settings are applied. One pair of AA batteries lasts therefore:
The power consumption of a Garmin InReach Satellite Pager is quite low even in tracking mode. When using it in the “Extended Tracking” mode the device consumes approximately 1 Wh per day. In the “Extended Tracking” mode the device sends the current position every 10 minutes, but Bluetooth and GPS recording remains deactivated. And of cause, switching the device off while not moving is advisable to maximize the battery life. If an InReach is use in emergencies only then normally no battery power is consumed. This means recharging the InReach on the trail is not necessarily required and can be avoided by minimizing the use i.e. by extending the tracking interval to 1 hour or deactivating tracking completely. Below the capacity of the internal Lithium-Ion battery and the approximate running time with 10-minute tracking in the “Extended Tracking” mode:
If a smartphone is used as the primary navigation device, then the actual energy consumption should be carefully tested before the hike to have a good knowledge how many recharges are required on the longest planned sections. This test should measure the actual energy consumption of the smartphone with continuous track recording as this is part of the terms and condition for using the track files. In the following comparison with GPS devices I will assume a daily energy consumption of 5 Wh per day if the smartphone is as primary navigation device what corresponds to one full battery charge for about 2 hiking days. Note, that the actual energy consumption with continuous recording may be even higher. For this reason I use my smartphone only as a backup navigation device in specific circumstances when reviewing satellite images or a high screen resolution is required. A basic handheld GPS simply consumes much less energy than a smartphone and minimizes therefore the total weight.
The additional energy consumption of a flash light and a camera (if carried in addition to the smartphone) adds to this energy bill.
Knowing your personal electrical energy consumption is important to correctly plan the required amount of batteries and to select the appropriate size of a power bank and/or power generation devices. Therefore I encourage every hiker that plans an adventure on the GPT to measure the actual power consumption of his devices before departing. The device running time with a full battery can be tested by selecting the to recommended power saving mode and simply monitor how long the device keeps running till the battery is depleted and the device faints out. This test verifies the actual capacity of the internal battery and the consumption of the device. When recharging the device, you can measure the power consumption by plugging an USB power monitor in between the USB charger and the tested device. These USB metering devices are cheep, simple to use and readily available online.
An inexpensive recommendable USB power monitor is the [http://portablepowersupplies.co.uk/home/premium-usb-dc-power-monitor PortaPow Dual USB Power Monitor ].
If you run low on power or navigate with your backup navigation device you should completely switched off the handheld GPS or put the smartphone in airplane mode and deactivate GPS recording whenever the route is sufficiently visible.
===Batteries and Power Banks===
The most versatile way to carry electrical energy are batteries. The following table shows the characteristics of commonly used and recommendable battery types and USB power banks.
{| class="wikitable"|+Battery and power bank specifications! Battery Type ! Stored Energy ! Weight ! Specific Stored Energy ! Nominal Voltage ! Actual Range ! Comment|-| colspan="7"|Rechargeable AA Batteries|-| AA NiMH Battery | 2.2 – 3.0 Wh 1’800 – 2’500 mAh | 25 g | 85 – 120 Wh/kg | 1.2 V | 1.4 – 1.1 V | New quality NiMH batteries have a capacity of 2’000 – 2’500 mAh but over time and with frequent use this drops.|-| colspan="7"|Non-Rechargeable AA Batteries|-| AA Alkaline Battery | 3.0 – 4.2 Wh 2’000 – 2’800 mAh | 23 g | 130 – 180 Wh/kg | 1.5 V | 1.6 – 1.1 V | Alkaline batteries are good for devices with a low power consumption (GPS).|-| AA Lithium Battery | 4.5 – 5.25 Wh 3’000 – 3’500 mAh | 15 g | 300 – 350 Wh/kg | 1.5 V | 1.8 – 1.5 V | Lithium batteries have the highest specific energy but are more costly.|-|colspan="7"| Other Rechargeable Batteries and Power Banks|-| Lithium-Ion Battery | Depending on size | Depending on size Approximately | Approximately 200 Wh/kg | 3.7 V | 4.1 – 3.7 V | Most devices with build in batteries have Lithium-Ion batteries installed.|-| 5000 mA Power Bank | Nominal 18.5 Wh Effective 13 - 15 Wh | 120 – 150 g Nominal| Nominal 125 – 200 Wh/kg Effective 100 – 160 Wh/kg | 5.0 V | 5.0 V | USB power banks are specified based on the capacity of the internal Lithium-Ion batteries (3.7 V) and not the output voltage (5.0 V) of the USB port.|-| 10’000 mA Power Bank | Nominal 37 Wh Effective 26 - 30 Wh | 180 – 240 g | Nominal 125 – 200 Wh/kg Effective 100 – 160 Wh/kg| 5.0 V | 5.0 V Table 113: Battery and | USB power bank specificationsbanks are specified based on the capacity of the internal Lithium-Ion batteries (3.7 V) and not the output voltage (5.0 V) of the USB port.|}
====Rechargeable NiMH Batteries====
[[File:discharge batteries.png|frame|NiMH battery discharge curve. For GPS devices the discharge current is typical 0.1 A or less therefore the highest curve of the diagram is applicable. Image: lygte-info.dk]]Be aware that the battery voltage depends on the charging state, the temperature and the load during use (consumer). When fully charged the voltage is slightly higher than the nominal voltage. During use the voltage drops. By measuring the voltage the battery state can be estimated.This is particular helpful when using rechargeable NiMH batteries. A fully charged NiMH battery provides 1.4 V at an ambient temperature of approx. 20 ºC (open-circuit voltage). At the beginning of the discharge cycle (first 10% of capacity) the voltage drops quickly to 1.3 V where the “plateau” starts. Once the plateau is reached the voltage slowly decreases during use to about 1.2 V (80% of capacity). When the battery is nearly empty the voltage drops again sharply (last 10% of capacity).
To maximize the life of rechargeable NiMH batteries the following should be observed:
I fabricated a tiny ultra-light voltmeter from simple of-the-shelf electronics that I use on my hikes to monitor the state of my NiMH batteries. This helps to combine batteries of a similar discharge stage to recharge these batteries effectively without overcharging them.
====Non-Rechargeable Alkaline Batteries====
====USB Power Banks====
The only lossless method to “recharge” a depleted device is changing batteries. This is one reason why I prefer a Garmin GPS device over smartphones. A battery change takes seconds and no electrical energy is lost.
In contrast, charging a smartphone or an InReach device with a USB power bank is not lossless. My measurements showed me that only 70% - 80% of the energy ends up in the charged battery and 20% - 30% of the energy is converted into useless heat during the energy transfer process. These losses are unavoidable due to the battery chemistry and the power consumption of the electronics in the power bank and the charged device. This means that a 10’000 mAh power bank with a rated capacity of 37 Wh equals 26 – 30 Wh in your smartphone and InReach. Therefore the effective specific stored energy of a USB power bank with Lithium-Ion batteries (100 – 160 Wh/kg) tends to be slightly lower than the specific stored energy of AA Alkaline batteries (130 – 180 Wh/kg) and not much better than NiMH batteries (75 – 120 Wh/kg). Non-rechargeable Lithium Batteries (300 – 350 Wh/kg) are clearly on top of the list when minimizing weight.
<small>Note: I estimate that about one third of the losses (7% to 10%) occur in the power bank by stepping up the voltage from the internal Lithium-Ion battery (3.7 V) to the USB voltage (5.0 V). The remaining two third of the losses (13% to 20%) occur in the charged device when transforming the USB voltage (5.0 V) into the appropriate charging voltage (4.25 V) for the internal Lithium-Ion battery and by losses in the charged battery itself (internal battery resistance). The rule of thumb is: As warmer your devices become while charging as higher are the losses.</small>
Calculation examples:
When using a USB power bank with Lithium-Ion batteries consider the following:
The Goal Zero Guide 10 plus AA NiMH battery charger can also be used as a power bank but the efficiency is much lower compared to a power bank with Lithium-Ion batteries. For more information to this gadget see the section about USB AA NiMH Battery Charger.
===USB Charger===
[[File:navegacion con GPS 8.JPG|thumb|Left: Standard in Chile (Type L, CEI 23-16 VII. Same as Italia and Uruguay) Center: Current Standard in Argentina (Type I, AS 3112. Same as Australia) Right: Older Standard in Argentina (Type C, Europlug)Image: Martín Lizondo]]A USB charger is required to recharge the smartphone and the USB power bank during resupply town visits. In Chile and Argentina, the same voltage and grit frequency is used (220 V / 50 Hz) but both nations have different sockets. In Chile a USB charger with an Europlug works perfectly fine. For Argentina an additional Type I adapter may be useful.
To shorten charging time a high-power 2 A charger is preferable over a standard 1 A USB charger. The weight difference is not significant. A1 A USB charger weights typically 30 g. A 2 A charger can be as light as 36 g.
===Solar Panels and Other Outdoor Power Generators===
To charge smartphones, AA NiMH batteries and power banks with solar power in a reasonable time a panel with a USB outlet and a power output of approximately 5 W is needed. Such a panel provides a charging current of 1 A when vertical alignment to the sun on a cloudless day and not too high ambient temperatures. It still supplies a few hundred mA under less favourable condition, i.e. when charging while hiking with the panel fixed to the backpack what normally results in a suboptimal alignment to the sun.
Bigger solar panels make only sense if you have an unusual high power consumption i.e. when:
Based on multiple tests I conclude that a good outdoor solar panel has a specific power generation of roughly 20 W/kg. So a panel with a 5 W power output weights around 250 g.
In addition to the solar panel a AA NiMH battery charger is required. I recommend the Goal Zero Guide 10 plus device that weights 64 g. The bonus feature of this device is that it can also be used as a USB power bank by discharging AA NiMH batteries. But the Goal Zero charger comes with the disadvantage that it charges only 4 NiMH batteries together. Alternatively use the EBL USB Quick Charger . The advantage of the EBL charger is that it charges individual batteries (a single battery if you want) and that it charges faster if you have enough USB power (i.e. if you have up to 2 A USB input current in towns or with a bigger solar panel). But the EBL charger can not be used as a power bank. The weight of the EBL charger is with 68 g nearly identical. For more information to these the section about USB AA NiMH chargers USB AA NiMH Battery Charger.
In addition, a sufficiently long Mini-USB cable is required. While charging, the batteries should not be “cooked” in the sunlight or the pocket on the back of the hot solar panel. There the batteries deteriorate quickly.
To charge four NiMH batteries while hiking you need two additional NiMH batteries for your GPS. So you must carry at least six NiMH batteries to have also enough backup power for a series of cloudy and rainy days.
So, a 5 W solar panel set with a charger, a cable and sufficient batteries weights at least 475 g:
This provides a good baseline to calculate the break-even point at which carrying a solar panel becomes beneficial. I do this by assembling hypothetical non-solar power supply sets of a similar weight. Only if all of these hypothetical sets would still be insufficient than a solar panel becomes beneficial.
Comparing the 5 W solar panel kid with these three non-solar options shows pretty clearly that the break even-point for a solar panel is far down the trail. Walking 10 to 15 days without resupplying is only required on the longest sections and a solar panel pays really off when exceeding this duration.
Conclusion 1: For someone that hikes light and fast a solar panel is rarely beneficial.
There are other motives that may make a solar panel beneficial: cost cutting, an unusual high power consumption on the trail, autarky and slowness.
Minimizing costs: A overnight town-stop with a proper bed is something that most hikers enjoy but hikers with a tight budget might prefer to just buy food and return to the trail immediately. A solar panel eliminates the dependence on power sockets what helps to cut town time and no money must be spend on batteries.
Unusual high power consumption: Smartphone junkies will suffer on the GPT as there is little connectivity. But some hikers will probably still find reasons and opportunities to spend “quality time” with their smartphone on the trail. A solar panel helps covering the resulting power consumption. This applies also to hikers that carry and use a tablet computer on the trail.
Autarky and slowness: The primary range limitation when hiking is food; it’s the fuel for the body and we can carry only a certain amount in our backpacks. If someone gets extra food along the trail, he extends his range and postpones the moment at which me must eventually bail out to resupply.
Resupplying at the section start or section end is often possible in the far north and in the south but from GPT05 to GPT12 and from section GPT19 to GPT21 hikers “normally” need to take a bus to get to a proper resupply town further away. Such a resupply trip can take up to 3 days.
I used the word “normally” because there is a trick how to remain on the trail in this particular scenic and hiking-friendly area: purchase food from the arrieros, the native Pehuenche and settlers that live during the summer on the trail. There are also a few kiosks or mini shops in the tiny settlements on the trail that sell some basic supplies. At the right time you may also harvest piñones on sections GPT10 to GPT16 which provides plenty of free carbohydrates. So, in these areas food is easier to obtain than electricity. If you have a solar panel to recharge your electronics you can use these unplannable opportunities to get some additional food to remain longer on the trail. We frequently use such informal resupplies to stay 2 to 3 weeks on the trail, often with relaxing “zero” and “nero” days in company with residents on the trail. Our solar panel helped us to keep our electronics fully charged to not worry about remaining power. When being a guest at a puesto a solar has a bonus feature: you can offer to charge the mobile phones of your hosts.
Conclusion 2: A solar panel adds autonomy and permits slowing down if you get enough extra calories on the trail.
Should you opt for a solar panel consider the following best practices and lessons learned:
A power monitor helps to recognize and to respond to this effect. If this happens simply unplug and replug the charged device. Smarter solar panels have build-in electronics that do this automatically.
With my mixed experience I’m reluctant to recommend a specific item or brand. I made reasonable good experiences with solar panels sold by Anker but they only offer panels that are a bit bigger and heavier than actually needed. The Anker “15 W” solar panel has a maximum output of about 8 W and the weight is close to 400 g. A bit oversized for a group of two.
====USB AA NiMH Battery Charger====
Any outdoor power generator requires in addition a suitable AA NiMH charger to use the generated electrical energy in a handheld GPS device. In the previous chapter I briefly mentioned the Goal Zero Guide 10 plus and the EBL USB Quick Charger .
If you carry a Goal Zero Guide 10 plus AA NiMH battery charger with your power generation device calculate with the following charging and discharging efficiencies and currents:
Even if you have more power available the Goal Zero charger will not “draw” more than 0.8 A from the USB port. This corresponds to 4 W. Therefore, a solar panel bigger than 5 W is only beneficial in suboptimal conditions if used with this AA NiMH battery charger (charging while hiking or charging in cloudy weather). Fully charging 4 depleted NiMH batteries takes around 4 to 6 hours depending on the battery capacity. Note that the charging rate towards the end of the charging cycle is relatively low. Therefore I often stop the charging when the green light starts blinking fast.
To fully charge 4 depleted AA NiMH batteries with a capacity of 2’000 mAh (4 x 2.4 Wh) roughly 14 to 15 Wh are required.
If using 4 fully charged AA NiMH batteries with a capacity of 2’000 mAh (4 x 2.4 Wh) roughly 6 to 7 Wh of USB power can be generated. If the charged USB device “draws” a lower current (0.5 A or less i.e. the InReach Mini) the energy transfer is more efficient (closer to 75%). Connecting bigger consumers (1 A or more like smartphones) makes the power bank mode of the Goal Zero charger rather inefficient (closer to 60%).
If carrying an EBL USB Quick Charger calculate with the following charging efficiencies and currents:
Fully charging 4 depleted NiMH batteries takes around 2 to 3.5 hours depending on the battery capacity.
To fully charge 4 depleted AA NiMH batteries with a capacity of 2’000 mAh (4 x 2.4 Wh) roughly 21 Wh are required.
====Bio Lite CampStove====
I recently stumbled in an outdoor shop over a piece of gear that also promises to charge electronics in the outdoors: the Bio Lite CampStove. This stove promises to produce electrical energy using the thermoelectric effect. All you need are small pieces of wood to recharge your gadgets while cooking with fire. Here the link: https://eu.bioliteenergy.com/products/campstove-2
This sounds cool? Certainly! But before getting excited let’s analyse it. The manufacturer specification states that the weight is 935 g and that the peak power output is 3 W. So, it would feel like a heavy stone in the backpack and when reading “peak power” I instantly know that I should not expect this output under normal conditions. So, let’s assume that an average power output of 2 W can be maintained over some time. 2 W out of 1 kg of gear means a specific power generation of 2 W/kg.
Compare it with a solar panel: A solar panel has 10 times the specific power output (20 W/kg). Therefore, a solar panel with the same power output would weight just 100 g and you do not need to throw constantly wood chips into it. I would go for the panel!
Let’s calculate how long it would take to charge a smartphone with a typical 2’000 mAh battery. 2’000 mAh corresponds to 7.4 Wh stored energy (you remember 2 Ah x 3.7 V = 7.4 Wh). If considering a charging efficiency of around 80% you need to produce at least 9 Wh of electrical energy to get if fully charged. With an average output of 2 W it would take 4 to 5 hours of keeping the stove running to recharge an empty smart phone. I would be annoyed!
A comparison with a power bank is even more embarrassing for the Bio Lite CampStove. A USB power bank of the same weight has an effective stored energy of up to 160 Wh. To produce the same amount of energy you need to run the Bio Lite CampStove somewhere around 100 h when assuming an average power output of 2 W and a charging efficiency of 80%.
If used 2 to 3 hours per day it produces only 4 to 6 Wh per day what would be barely be enough to keep a GPS and a InReach device running (considering the Goal Zero Charging Efficiency of 65% to 70%).
I can look at this piece of gear from whatever angle and I can’t see under what circumstances it provides a true benefit. Therefore, carrying the Bio Lite CampStove on a hike proves only the inability or unwillingness to analyse. So, for me this is a useless toy for adults that want to play the outdoor guy!
====WaterLily Turbine====
There is another power generator that recently pushed on the market: the WaterLily Turbine. The designers suggest using it in fast flowing rivers or hung up in a tree to harvest wind energy. Here the link: https://waterlilyturbine.com/products/waterlily-turbine .
According to the manufacturers specification the weight is 1.3 kg and the peak power output is 15 W. Again, peak power means that a bit less should be expected. I will assume an average power generation of 10 W for my analysis. With 1.3 kg it’s heavy but with approximately 10 W output it produces more than a trickle charge.
The specific power generation of the WaterLily Turbine is 8 W/kg. Much better than the Bio Lite CampStove (2 W/kg) but still inferior to solar panels (20 W/kg). Therefore there is no reason to carry this turbine in areas with enough sunshine. Solar panels come with the additional benefit that you can choose the size you actually need. This does not apply to the turbine; you can’t carry half the turbine if you just need half the power.
The advantage of this turbine is that it works without constant attention like a solar panel and unlike like the Bio Lite CampStove that needs to be constantly feed with wood chips. So, someone can set it up when pitching camp and let it run over night hoping that it does not rain too heavy to find the turbine in the morning blocked by leaves and twigs or even flushed away.
If used every second night for 10 hours it produces 100 Wh per use or 50 Wh per day in average. Finding every night a spot with suitable conditions for this gear is not realistic and 50 Wh per day is still much more than a typical hiker or packrafter possibly needs. So in most cases it would be overkill.
Let’s compare this turbine with a power bank of the same weight. 1.3 kg of power banks store up to 200 Wh effective energy. This corresponds to running the turbine twice for 10 hours. That’s not bad but only useful if you really need a lot of electrical power. And I mean a lot!
So the WaterLily Turbine is no complete non-sense like the Bio Lite CampStove. But carrying this turbine only pays of under very specific circumstances. It makes only sense in regions with insufficient sunshine. This might be the case when packrafting or seakayaking in the Patagonian fjords otherwise a solar panel is more effective and practical. And it is only beneficial on a rather long trip of a bigger group or for activities that require lots of electrical power i.e. when filming with (semi-)professional gear.
==Conclusion==
The previous analysis showed that there is no “one-size-fits-all-solution” but that hikers must make individual choices that match personal preferences and hiking habits. Also the chosen sections should be considered. Sunshine is frequent in the north (GPT01 to GPT15) and on the Argentine side (GPT23 to GPT26) making a solar panel more beneficial on these sections. In other areas someone might have bad luck and be pursuit by clouds and rain for a week or even more.
