Efficient Battery Practices

1. mAh is the best metric I’m aware of.
2. The faster you charge, the more voltage is lost in resistance and diffusion.  While the newer batteries are much better at charging and discharging quickly without losing as much efficiency, all batteries are more efficient if charged / discharged more slowly.
3. Cold batteries have more losses when charging / discharging (diffusion of the ions in solution occurs more slowly).  The charge doesn’t go away if you’re not drawing current.  And it’s much less of an effect at low current draws.  And many lithium battery chemistries tolerate much lower temperatures than alkaline or NiCad batteries did.

Thanks so much for your quick and thoughtful reply. This is very helpful.

Battery brick manufacturers lie about capacity.  A lot.  You don’t get 10,000 mAh out of a “10,000-mAh” battery.  The name-brand companies lie less than the cheaper vendors on eBay, but go by trusted reviews and your own testing of how long / how many recharges you can get from a battery.

I use one of these to 1) check different wall and car chargers, 2) compare different cables, 3) measure the charging rates of usb-headlamps, UV water treatment, etc, 4) measure and integrate the input and output of battery banks ($1.48 US including shipping, alternates between voltage and amp readings):

https://www.ebay.com/itm/USB-Charger-Doctor-Current-Voltage-Charging-Detector-battery-Voltmeter-Ammeter/173445783351?hash=item28622c9f37:g:aTUAAOSwvylbYqxg

The style below (costs more at $11, but) appears to integrate amps into amp-hours which would be REALLY handy when putting a battery brick through its paces and free you to do other stuff rather than recording amps every 5-10 minutes during multiple recharges.

https://www.amazon.com/Eversame-Multimeter-Voltmeter-Thermometer-Electricity/dp/B071KVBSXG/ref=asc_df_B071KVBSXG/?tag=hyprod-20&linkCode=df0&hvadid=309722091285&hvpos=1o4&hvnetw=g&hvrand=14180224845324476496&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033901&hvtargid=pla-568017420926&psc=1&tag=&ref=&adgrpid=60439548223&hvpone=&hvptwo=&hvadid=309722091285&hvpos=1o4&hvnetw=g&hvrand=14180224845324476496&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033901&hvtargid=pla-568017420926

Edited to add: when I first checked all my car chargers and cables, I found out I hadn’t been imagining that sometimes my phone would charge VERY slowly.  When testing them, I’d switch meter and cable and phone from one charger to another (so the only difference was the charger) and see perhaps 0.92 amps from one charger and 0.18 amps from another.  So I threw away the crappiest chargers and life had been better ever since.

I like these 3-way charging cables ($10-ish on eBay) both while traveling and while backpacking.  I can charge several things at once as long as too many of them aren’t high-amp demands that exceed the charger’s output. Say, a phone, a UV SteriPen, and bluetooth earbuds, charging all at once.

A decently wide, strong but not huge rubber band (as is used to hold 2-3 stalks of broccoli together in the store) is really nice for strapping your phone to your battery brick into one unit so you can use it while it charges as you hike.

Thanks again, all really helpful!

David’s got it.  +1 on the meter and testing your setup before hitting the trail.

One point I always make about batteries.  Quick charge from marketing/ads almost always means it will charge your device from the battery quickly.  Hikers are more interested in how quickly we can charge the battery pack at an outlet, and less about how quickly I can charge my phone from that battery pack.  Anker and RavPower sometimes talk about accelerated charging (of the battery).  The key here is to have a battery that will accept a quick charge and a charger that will supply it.  Anything above the USB standard requires compliant communication between the charger and battery pack, so I would do the research, stick with the name brands, buy the same brand charger or pack.   And then test it.

Personal choice of course, but wired earbuds and a solar-charged watch?…just sayin’.

I’ll probably get one of those Garmin watches one day.  I use an Apple Watch every day, except when I’m hiking or swiming.  Then I pull out the trusty timex ironman watch

+1 on previous

Anker 10,000 is pretty popular.  Since many people say they have it, including me, it must be fairly reliable.

The 10,000 mAh rating is of the 3.7 V lithium battery that’s contained inside.  The USB voltage is 5 V so you have to multiply the 10,000 by 3.5 / 5 to get the mAh of USB voltage as measured with one of those meters.  And subtract some for inefficiency and deviation from spec.

Probably the best is to actually try one at home.  Try a 10,000 mAh power bank and see if it has enough capacity, and then size up or down from there if needed.  Like, if it’s still half full after you charge everything, maybe get a 7,000 mAh instead – make sure you have a little extra capacity for reserve.

“The 10,000 mAh rating is of the 3.7 V lithium battery that’s contained inside. “

I’ve heard that before and I don’t doubt that is their rationalization.  Like the 11-amp table, 120-volt Sears saw that is “5 peak horsepower” because it delivers 5 hp for a fraction of a second due to the momentum of the motor and blade.  Or, to claim the starting battery in my car can do 3000 cold-cranking amps because it produces 500 amps (at 2.2 volts ) in the first cell), plus 500 amps at 2.2 volts in the second cell, plus 500 amps. . .

It’s a lie.  And some vendors lie more than others.  So test any battery bank.

Agreed, the Anker “10,000 mAh” is popular.  Look at reviews for how many times it can charge your particular devices.

More so, practice minimizing usage and power consumption by your devices.  What more does one need than a headlamp on a FKT?  Time spent looking at your devices, vlogging, emailing, etc, just wastes time that could be spent hiking or sleeping.

I get your point about deceitful advertising

But that’s how all power bank manufacturers spec them, the mAh of the Lithium battery.  It would be a little more clear if they said it was the battery.  At least most manufacturers are consistent.

the mAh value isn’t really all that intuitive though.  They have the number of times it will charge specific phones which is easier for people to comprehend.  I think that number is pretty honest.

A different example – the U.S. standard for down loft is a bit inflated compared to the European standard which is fairly consistent with reality.  The U.S. standard is deceitful.  Or temperature rating of a sleeping bag if they don’t use the European standard.

I often see confusion when people use mAh to compare batteries and battery packs, because it measures current and time at an unspecified voltage – not energy, which is what we (mostly) care about.

Milliwatt-hours are real energy units, independent of the current and voltage(s) involved. A 10,000 mAh battery at 3.7 volts is 3.7 x 10,000 = 37,000 milliwatt-hours or 37 watt-hours. Another battery rated for 10,000 mAh at 5 volts (USB standard voltage) holds 50,000 milliwatt-hours or 50 watt-hours, and so on.

The hard part is knowing what voltage the battery pack maker used for computing mAh. Usually they don’t say.

And there are charging and discharging energy losses, which vary by temperature and charging/discharging speed and target device.

And then there is, umm, stretching the truth by battery pack makers, sometimes a lot.

Some device makers – phones, headlamps, etc. – will state the milliwatt-hours stored in the device, which can help.

But as David said, the only way to really know is to buy a meter and test your devices and your battery pack under your anticipated conditions.

To restate David’s advice as some rules of thumb:

– If you want to save time in town, buy battery packs that can be charged as fast as possible from powerful chargers. (Except they won’t charge any faster from standard or crappy chargers.)

– Charge devices like phones and headlamps from your battery pack in warm conditions – not too hot, not too cold

– Charge devices like phones and headlamps from your battery pack slowly, typically standard USB rates of 0.5 to 1 amp and 5 volts.

– With modern lithium batteries, don’t worry about cold temperatures (within reason) for storage or use.

And I’ll add

– Don’t run devices down to 0% – stop around 10% or the last “bar”. Running down to 0% can sometimes cause harm; and many charge indicators give unpleasant surprises as you get close to 0 (“but I had 10% only 5 minutes ago and it’s dead now!”)

– Try not to charge devices past 90% from your battery pack. Charging that last 10% from 90 to 100 takes a lot more energy than from 80 to 90 due to battery inefficiencies. This is kind of a pain because you can’t plug-and-forget.

Hope this helps.

— Rex

Thank you all again for this great advice. Really appreciate the rules of thumb, Rex.

David and Bob, re: energy usage and the FKT. I use three methods of recording the track: inreach, gps watch and phone (on airplane mode with Gaia). I know it seems counterintuitive to have that much energy use, but this is my third attempt and I’ve put a lot of time in training and I need to have multiple backups. I also use the data for pacing purposes. As far as earphones, there are just points during the trip that I need to zone out, as I’ll be hiking 18-20 hours a day for over 6 days. I think wired earphone use more energy from the phone than bluetooth, but more importantly, I like to use my Aftershokz as they enable me to hear my surroundings as well.

Thanks for all the battery help. I’ve trimmed down my kit to the bare essentials, but need to nail the battery thing.

18-20 hours a day for 6 days, wow!

hopefully you’ll post here when you do this.  Posting while you’re doing it would be cool but you will probably be too busy

Thanks, I’ll have a link to my inreach, and will try to remember to share it. I will have it up on fastestknowntime.com. It will be my third attempt at the Long Trail unsupported record.

Eli – If you have sorted out all the battery stuff, can you share what the unsupported FKT is for the LT?  How did the first two attempts end – injury (my usual fate) or too much time?  Beyond all else – GOOD LUCK! We’ll be watching and hoping for success.

Not sure if I should go too off topic in this post, but quick info re: LT FKT. The unsupported FKT (only thing I can get along the way is water) is 6 days 17 hours and 25 minutes and is held by Travis Wildeboer (he’s a Barkley finisher), and is over a decade old. In 2016, I took a nasty fall on day one, tried to regain ground on day two and completely blew up. In 2017, I was just too slow. Couldn’t take in calories on days 3-4 and got way behind. Still finished for the heck of it in 8 and a half days. Feeling good this year! Going for it in last week of June.

(I freak out about the battery stuff because in 2017, I took too long, didn’t have enough battery juice and ended up needing someone to bring me a battery for my headlamp, so not officially unsupported, but by then I knew I didn’t have it anyway.)