UNSUPPORTED: how to recharge phone, SPOT, headlamp?

Like Nick said, mAh are not a unit of energy without knowing voltage. Most rechargeable batteries have 3.6 to 3.85 volts measured inside devices. Multiply mAh by 3.7 then divide by 1,000 to roughly get Watt-hours (Wh).

Battery packs should have Wh labels in order to pass through TSA. Finding mAh or Wh for other devices is hard.

But knowing Watt-hours at hidden battery terminals doesn’t include energy losses going from one battery to another. That waste could be as high as 30%, but measurements are rare.

This diagram shows the major energy losses using a battery pack to recharge another device:

Can’t do much about voltage conversion losses: 3.7 V to 5 V USB back to 3.7 V. Long, skinny, damaged USB cables lose a lot more energy than short, fat, healthy cables. Another area with very little testing. Short Anker cables seem like a good bet.

That wasted energy turns into heat. A battery pack or smartphone gets warmer while recharging. Cheap or damaged USB cables get warm, too.

— Rex

I just bought a 10,000mAh battery bank, ran my phone down, them timed how long to recharge the phone, and then ran my phone down again, and charged again until my battery bank was finished. Then I knew how many times the battery bank would recharge the phone.

I like this approach because it treats the system as a whole and takes into account any losses with the cables you are using without spending a lot of time doing calculations (nothing wrong with that for people that like doing that).

I’m under the impression that the first and last ~20% of charging (0–20% and 80–100%) is less efficient. Can someone confirm that? If so, doing your tests from 0–100% is somewhat less efficient but I like that it would give a little bit of extra margin assuming you kept the device between 20 and 80% in the field.

Loving the info in Nick’s and Rex’s posts.  Lead me to this conversion calculator and to learning/understanding more about battery capacity.  Definitely going to affect my future battery bank evaluation and purchase decisions.

Finding out how many times you can recharge your phone from your battery bank is a good idea. Also would be good to include headlamp and any other electronics being used.

However , that only shows capacity of the bank. It does not show the likely draw as you don’t know how often you will check your phone, take pics, use your headlamp and any other activity. Knowing that shows how quickly you will need than power bank. Could be 3-4 days or it could be longer. Or use it a lot and need to recharge every day. I use the phone as the primary example as it most likely is the chief power draw for the average backpacker.

This also doesn’t include temperature and a few other issues can can occur.

So settle on how often you will likely check your location, how many photos you will limit yourself to, how long in airplane mode, and other likely use, and then test your phone life in those modes which gives some idea of that side of the equation.

Then you can guess how long you can go before recharging and multiply that by the times the bank will recharge you and add some safety (10-20%).

With some assumptions, the math isn’t too bad. Need answers to a few questions first.

For each rechargeable device:
– How often will you fully recharge it on your trip?
– How many Wh (or mAh x 3.7 / 1000) does the internal battery hold?

Example for a 14-day unsupported trip, starting with fully charged devices:

iPhone SE 3rd generation, 3 recharges, 7.8 Wh battery
SPOT Gen4 Satellite Messenger or SPOT Trace, uses AAA batteries, not applicable
Nitecore NU25 headlamp, 6 recharges (night hiking), 650 mAh or 2.4 Wh battery

(3 x 7.8) + (6 x 2.4) = 37.8 Wh energy needed at internal batteries

Add 30% for worst-case energy loss: 37.8 x 1.30 = 49.1 Wh energy needed from inside battery pack

Some battery pack scenarios:

Nitecore NB10000 Gen 2 x2
Total 77 Wh, 27.9 Wh “extra,” 10.6 ounces (300 grams)

Nitecore Carbo 20000
Total 77 Wh, 27.9 Wh “extra,” 10.4 ounces (296 grams)

Nitecore NB10000 Gen 2 + Nitecore NPB1
Total 56.7 Wh, 7.6 Wh “extra,” 9 ounces (255 grams)

Hope this helps.

— Rex

Finding out how many times you can recharge your phone from your battery bank is a good idea. Also would be good to include headlamp and any other electronics being used.

However , that only shows capacity of the bank. It does not show the likely draw as you don’t know how often you will check your phone, take pics, use your headlamp and any other activity. Knowing that shows how quickly you will need than power bank. Could be 3-4 days or it could be longer. Or use it a lot and need to recharge every day. I use the phone as the primary example as it most likely is the chief power draw for the average backpacker.

Yes.

The best way is to monitor (measure) electrical use under the same conditions as one will be using the devices in the field. This can be time consuming.

I have been using solar and a battery bank on my campers for 20 years. I have never had a dead battery, even when camping for up to a month. I know how much electricity I will use daily, the most being in winter. Plus in winter I get the lowest amount of sunlight for my solar system. My battery banks are sized to provide 5 days of power — assuming it will be raining 24/7 in winter. If it rains more, I’ll just go home. The key here is I have a sophisticated battery monitor that measures amps into the battery bank and amps out. So I always know what percent of battery capacity is available. I rarely check the status because over time I confirmed it works.

I have two astronomy set ups for astrophotography. Two mounts. On each mount I have a small camera to guide the mount as it tracks the rotation of the earth. Each has a large cooled astrophotography camera connected to a telescope that is set to maintain a constant 32° F temperature. Each mount has two motors that are continuously adjusted every 1 – 2.5 seconds to keep my target centered. I also have a mini PC and a router at each mount for remote control. Finally I have electronic focusers on each telescope that periodically re-focuses. Everything is 12 volt except the routers and focusers, which are 5V.

I image almost every night from astronomical night until astronomical dawn. The longest nights are in December and the shortest in June. In June the cooled cameras use much more power than they do in winter. As it turns out, in winter and in summer both mounts consume 22 – 23 AH, or 264 – 276 watt-hours. It did this test with main power from the house to a 12V regulated power supply and a meter. Once I had the data, I built a battery bank for each mount. I used three 16AH LiFePo4 batteries wired in parallel for each battery bank, giving me a capacity of of 48AH at 12.8V or 614 wH. This way I can go two nights without charging, although 99% of the time I recharge each morning. When camping and doing astrophotography I connect both mounts to the trailer battery, which is 300AH at 12.8V or 3840 wH. LiFePo4 can withstand the most discharge cycles of any battery type and going down to 0% charge won’t hurt them. However they can’t be charged at temps below freezing.

Most of the small popular battery banks are Li-io and pack a lot of energy in a small package, but are not as safe as LiFePo4 chemistry.

The bottom line is to measure your use. Or buy a battery bank that is larger than you can possibly use over a period of time and just deal with the extra weight.

“However , that only shows capacity of the bank. It does not show the likely draw as you don’t know how often you will check your phone, take pics, use your headlamp and any other activity. Knowing that shows how quickly you will need than power bank. ”

Sure… but… how would you know how often  you use your gizmos until you go on a backpack? And… are you sizing your battery pack to some known or estimated  usage… or are you adjusting your usage to your battery pack?

If I start with fully charged phone, and I know my battery pack can recharge my phone twice and I have a 6 day backpack. Then I know that I need to adjust my usage such that I don’t run the phone down quicker than every two days.

“Let’s face it, today more and more people want to take fancy electronic devices. Nothing wrong with that…”

Rex, speak for yourself! (And yes, I’m kidding.)

this is a lost cause, but I still can’t help but suggesting a true minimalist approach to on-trail backpacking, at least. No electronic devices, except possibly a kindle for reading purposes only. Why? More opportunity for undistracted immersion in the wild. It takes days, at least, for our hearts and minds to settle into the new mountain/desert environment. Devices keep us distracted and attached to our normal at home routines. Worse: While hiking, we’re worrying about our devices. The trip almost becomes ABOUT our devices. They also act as a security blanket. A deeper part of going into the wilderness is to arrive at a sense of home, of belonging. That requires feeling safe, and trusting the environment without barriers. We all the know the phrase, “carrying our fears”. Simplicity brings one more readily into trust.

Is this simple?:

“Example for a 14-day unsupported trip, starting with fully charged devices:

iPhone SE 3rd generation, 3 recharges, 7.8 Wh battery
SPOT Gen4 Satellite Messenger or SPOT Trace, uses AAA batteries, not applicable
Nitecore NU25 headlamp, 6 recharges (night hiking), 650 mAh or 2.4 Wh battery

(3 x 7.8) + (6 x 2.4) = 37.8 Wh energy needed at internal batteries

Add 30% for worst-case energy loss: 37.8 x 1.30 = 49.1 Wh energy needed from inside battery pack

Some battery pack scenarios:

Nitecore NB10000 Gen 2 x2
Total 77 Wh, 27.9 Wh “extra,” 10.6 ounces (300 grams)

Nitecore Carbo 20000
Total 77 Wh, 27.9 Wh “extra,” 10.4 ounces (296 grams)

Nitecore NB10000 Gen 2 + Nitecore NPB1
Total 56.7 Wh, 7.6 Wh “extra,” 9 ounces (255 grams)”

Of course, for long off piste trips where there’s real danger, and one is travelling alone with no trails, these devices can be a godsend. No argument there!

this is a lost cause, but I still can’t help but suggesting a true minimalist approach to on-trail backpacking, at least. No electronic devices, except possibly a kindle for reading purposes only. Why? More opportunity for undistracted immersion in the wild. It takes days, at least, for our hearts and minds to settle into the new mountain/desert environment. Devices keep us distracted and attached to our normal at home routines. Worse: While hiking, we’re worrying about our devices. The trip almost becomes ABOUT our devices. They also act as a security blanket. A deeper part of going into the wilderness is to arrive at a sense of home, of belonging. That requires feeling safe, and trusting the environment without barriers. We all the know the phrase, “carrying our fears”. Simplicity brings one more readily into trust.

A Kindle on a backpacking trip? Blasphemy, I say!!

I take a headlamp and sometimes a camera. That’s it. I’ve played with cell phones and GPS, and they’re umbilical cords to civilization and I don’t like them (for me).

John Muir would probably tell you that a USGS map and baseplate compass is high tech that needs to stay at home, along with a lot of other stuff all of us now consider essentials.

A lot of people like their electronics. Plain and simple. Some people even take a double wall tent when they could just sleep under the stars and be more connected to the environment. Blasphemy, I say !!

Here’s the great thing about backpacking — each of us gets to do it the way we like — and for each of us it is the right way.

I’ve hiked with folks who brought a smart phone, SPOT, and even a chair! We all had a good time and their electronics didn’t interfere with my enjoyment. In fact, a couple times their phone made route finding quicker, while I was still unfolding my paper map.

I’ll stick to my “minimalist” ways, without passing judgement on how others want to enjoy the backcountry.

All true, Nick. I didn’t mean to be judgmental. As I said at the start, I was “suggesting” a more minimalist approach and began to explain why.  Many have never experienced this.

I typically always carry an iPhone 11 and a Zoleo messenger. Add a charging cable and a battery for longer trips.

I think the distraction, fuss, and clutter of carrying electronics is being grossly exaggerated compared to my experience.

Pull it out of my pocket, snap a picture, done. Probably faster than a film camera.

Pull it out of my pocket, check a bearing or contour, put it away. Probably faster than unfolding and orienting a map.

Charging? Plug in a cord and forget about it.

Electronic devices don’t turn us into drooling, fidgeting zombies unless we let them.

Roger: I’ve been gifting those little $10 USB testers as stocking stuffers for years now.  By putting them in line while charging a phone (or other device) in the same state of charge, you can compare cables and vehicle-power-port or home chargers to each other.  I’d had a vague sense of some chargers or charger/cable combos working MUCH slower than others – like seemingly not even keeping up with usage.

Putting the meter on it showed that some chargers were going at 0.17 amps with others were 0.93 amps, everything else being equal.  Sometimes the $1.13 chargers off of eBay aren’t worth the $1.13.  Throwing them away and replacing them with higher amperage units reduced all those frustrations.

So the meter is most useful for a day after you get it until you’ve tested all your charging paraphernalia and chucked the worst of it.

I’ve also used it to manually totalize the amp-hours from a battery or to a charging device by setting a beep to go off every 10 minutes and jotting down the amps.   Time-lapse photography with a smart phone would be more hands-off.

Sometimes the $1.13 chargers off of eBay aren’t worth the $1.13.
Yeah, with cheap consumer-grade stuff I have found it best to skip the bottom of the pool and move up the price range bit – with exceptions.

Sometimes the bottom of the pool seem to be selling the same thing as the mid-levels. Sometimes this is because the vendor is off-loading the last of his stock, sometimes the stuff may be a shade hot, and sometimes the really cheap stuff just looks like the better stuff. Differentiating between them is a game.

Cheers

Digital camera batteries at $1.73 off of eBay seem to work as well as the $29.95 ones sold in camera shops and allow you to bring several charged ones for a long trip instead of fiddling with chargers and PV panels.

LED dome/map lights I got for cheap have worked fine for years (and greatly increase the time before you drain your battery if you leave them on – from hours to days) but the cheap LED taillights didn’t last – I got pulled over (and let off) for no taillights a few months after I’d installed them – I don’t know how long they’d been bad.  Different use scenerios – minutes of use, versus hundreds of hours of use, but I’d been going for that supposed advantage of LED – they essentially never burn out.

Hi D avid

Yeah, ebay camera batteries is my route too. Much simpler, and more reliable too.

Your taillights: was it in fact the LED taillights which had failed? Did you test them once removed? I ask because I have also seen cheap relays and switches fail – for a rather unexpected reason. Tech discourse follows:

When you switch an incandescent light on there is a huge surge of current as the filament heats up and, then the current drops when the filament is hot. This current surge ‘blasts’ the mechanical contacts and keeps them clean. Domestic light switches have a wiping contact (usually brass on brass) rather then a simple butt contact, for this reason.

But when you switch a LED on there is no current surge. The contact surface of cheap relays and switches is usually a bit ‘dirty’, and this dirt can build up and be enough to prevent any current flow. Sounds weird, but so it is. Gold-plated contacts are needed for digital signals (see inside of PC).

I have a similar problem with an industrial emergency stop switch (rotate to release) on my CNC. It is designed for 660 VAC 15 A. On my CNC it switches 24 VDC at <10 mA. I had to put an external load on it to get it to switch reliably. I can get good gold-plated switches easily enough, but not with the rotate-to-release design. Problems, problems.

Cheers

. . . but the cheap LED taillights didn’t last – I got pulled over (and let off) for no taillights a few months after I’d installed them – I don’t know how long they’d been bad.

Often load resistors are needed when switching to LED brake, tail/turn signal bulbs.

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