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Does it save power to charge phone to just 80%?


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Home Forums Gear Forums Gear (General) Does it save power to charge phone to just 80%?

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  • #3747847
    Jerry Adams
    BPL Member

    @retiredjerry

    Locale: Oregon and Washington

    I got one of Rex’s USB meters that measure mWh when charging phone from USB power supply

    I have a Galaxy S9 phone and an Anker 20,000 mAh USB power supply

    Rex said that a phone’s lithium battery will have a longer lifetime if you never charge it above 80% or let it go below 30%.  I wonder if that would also save USB power supply life when charging the phone?

    I use about 50% of my phone battery per day.  I could charge it back up to 100% at the end of the day and let it run down to 50% the next day, or I could do 80% and 30%.  Would that save significant energy from the USB power supply?

    I charged phone to 100%.  Ran Gaia with the display on so maybe the load was constant.  It took:

    65.8 min to go from 100% to 80%

    126.8 min to go from 80% to 50%

    73.1 min to go from 50% to 30%

    Then I charged it back up and recorded mWh:

    2156 mWh to go from 30% to 50%

    3305 mWh to go from 50% to 80%

    2235 mWh to go from 80% to 100%

    % is not linear with actual power consumed.  100% to 80% took 65.8 min.  50% to 30% took 73.1 min.  Charging form 30% to 50% resulted in more minutes of run time than 80% to 100%.  So I corrected for that – 2156 mWh * 65.8 / 73.1 = 1941 mWh to get the same amount of run time.

    Using that correction, it took 5540 mWh to charge from 50% to 100%.  5246 mWh to go from corrected 30% to 80%.  5246 / 5540 = 0.95 – it saves 5% of power if you charge from 30% to 80% each day, vs charging from 50% to 100%.

    So, bottom line, it doesn’t really make enough difference to worry about.  But, it saves a little.  When I’m charging phone, if I notice it’s above 80% I’ll turn it off, but don’t worry much.  When it get’s to 100%, it will continue to trickle even though it’s not adding to the phone charge so turn it off then.

    Aside – if you could possibly be in a survival situation, you should charge to 100%.  Obviously.

    #3748363
    Brad W
    BPL Member

    @rocko99

    Interesting. Since listening to the podcasts on batteries I am not leaving any device plugged in overnight/while I sleep. I have already noticed a difference. Not sure if the NB1000 was more susceptible to this plugged in overnight drain but I have changed my habits.

    #3748402
    Rex Sanders
    BPL Member

    @rex

    Most smartphones slowly ramp up and ramp down recharging power in order to extend battery lifespan, at the expense of total recharge time.

    As Jerry measured, that barely affects the energy consumed. Thanks!

    Based on my not-yet-published measurements of battery packs other than the Nitecore NB1000, the overnight energy waste is an iPhone problem (at least), not a battery pack problem.

    Best advice is what Brad is following: unplug when full, usually a couple hours or less. Don’t let devices stay plugged into portable battery chargers overnight.

    — Rex

    “A watt-hour here, a watt-hour there, and pretty soon you’re talking real energy.”

    #3748415
    YoPrawn
    Spectator

    @johan-river

    Locale: Cascadia

    Never thought of the power savings, but I always charged to 80% for the health of my battery.

    I have an original iPhone SE (2016) and it still has 90% battery capacity, so I think it works quite well. :)

    #3748568
    Dan @ Durston Gear
    BPL Member

    @dandydan

    Locale: Canadian Rockies

    My phone occasionally burns a lot of power either because it’s getting wet and turning the screen on constantly, or an app is kinda crashing/stuck in a loop and working hard. So on trips where power is precious I like to charge lower – only about 50% – to avoid having all my “eggs in one basket”.

    #3748569
    David Thomas
    BPL Member

    @davidinkenai

    Locale: North Woods. Far North.

    I bought* the largest lithium battery for 2000 miles around (until you get to Moss Landing in California). 46.5 MW and 93 MWh (or, if you prefer it in Anker units, 93,000,000,000 mWh).  Enough energy to recharge my iPhone 12 fully, twice a day, for 12,300 years.  Alas, it’s not very portable.

    If you cycle it fully (charge it from the grid and discharge it to the grid), it is 85% round-trip efficient – 15% of the energy goes away in charging and discharging.  If OTOH, when cycled between 70 and 85%, it is 93% efficient, roundtrip.

    I’m more interested in its losses if used at 20 MW versus at 46 MW, but I haven’t gleaned that information yet.

    * I was the deciding vote among 9 directors.  It wasn’t my $40M.

    #3748628
    Roger Caffin
    BPL Member

    @rcaffin

    Locale: Wollemi & Kosciusko NPs, Europe

    You won’t regret it.
    Neither will they.

    Cheers

    #3748635
    Rex Sanders
    BPL Member

    @rex

    The Moss Landing giant pile-o-batteries keeps popping up in the local news due to fires or overheating. Hope your local fire department is well-equipped and well-trained on dealing with these problems.

    And with extremely rare exceptions, you don’t need to worry about a mainstream smartphone battery or battery pack catching fire or exploding. Unless you drop it into the campfire :-)

    — Rex

    https://www.montereycountyweekly.com/blogs/news_blog/moss-landing-battery-plant-down-indefinitely-after-second-incident-in-5-months/article_fd119cb6-8ec6-11ec-882f-db4faf6c0495.html

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