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Battery life: real world burn rates vs specs

derek87
over 3 years ago

as usual, i'm coming at this from a perspective of having had the Forerunner 935 for more than 4 years. when i bought it, it was advertised as having up to 2 weeks smartwatch mode and up to 24 hour of GPS activities.

in the time i had it, i would say the 935 lived up to those specs and then some, even with me using a 3rd party watch face (JBlack) that displays seconds and HR at 1hz. even now at 4 years (still running FW13.00 which probably helps), i still see a roughly 4.5%/hr burn rate for GPS activity (1 sec recording, no GLONASS nor Galileo) and about 6+%/day for smartwatch mode (no notification alerts except for phone call). in the few instances when i was sick and inactive (not using GPS), it would always see a projection of 16 days of battery life in smartwatch mode.

the 945LTE has on paper, better specs than the 935 for battery duration under GPS usage, but i'm finding things to be significantly below spec. i admittedly only have a few hours of GPS measurements under my belt, but in similar settings as my 935, i'm estimating burn rate to be about 4%/hr which is about what i got with my 935 when new. nowhere near the 3%/hr that the 35 hours spec suggestions: . i don't see how i would get close to the 35 hour spec. perhaps, i will need to do a long duration, multi hour activity like a hike during my backpacking trip to get a more accurate numbers because it appears the updated version of the excelled BatteryMonitor widget seems to only round the reported battery percentage. (the old version on my 935 would report, perhaps somewhat inaccurately, the percentage to the nearest tenth)

similarly, the 945LTE, from again limited date, seems to burn through about 9-10% day in smart watch mode. so in this case, it will last less than my 935.

these aren't showstoppers by any stretch as the projected 24 hours of GPS will be enough for my backpacking trip and i can charge every 6-7 days rather than 8-10 days with my 935, but i'm a little disappointed.

i wonder if the battery capacity of the 945LTE is less than the 935, or perhaps the newer processor is a bit more power hungry.

i should note that i have PulseOx and wifi and LTE disabled, and while it's not an apples to apples comparison, i'm essentially running the same stuff (widgets and settings) as i am on my 935 but there are new things like the Body Battery that may or may not be using more power up.

what are your experiences? do you think the specs are legit? i know they say "up to"... i wonder if i should try a bare bones watch face with no seconds displayed and see what the basic burn rate is.

  • 0 over 3 years ago

    I will try to use a widget to monitor / log numbers more reliably, but anecdotally I feel like the discharge rate is higher than I'd expect.  My activities are kind of all over the map though with some indoor rides, GPS runs w/ phone (no LTE), GPS runs w/ LTE etc...

    Recent numbers:

    • Overnight w/ pulseox: ~14% / day rate estimated by Battery Info widget
    • 90 minute indoor spin: ~1.5% used (per fit file data), estimated full capacity 83.33 hours
    • 90 minute GPS run w/ LTE:: 13% used (per fit file data), estimated full capacity 12.18 hours
    • ~30 minute open water swim, phone in buoy, unsure if LTE was running: 13% used, estimated capacity 6 hours
    • ~30 minute open water swim, no phone in buoy, LTE probably on: 4% used, estimated capacity 14.58 hours
    • 27 minute open water swim, no phone in buoy, LTE should be on but no LiveTrack received: 10% used, estimated capacity 3.4 hours
    • 1:15 triathlon, no phone on me, LTE on: 14% used, estimated capacity 8.93 hours
    • 3:40 ride (elapsed time 4:10, 3x flat tires, water stops), BLE, No LTE, GPS+GLONASS, Power Meter, HRM, Varia: 15% used, estimated capacity 28.89 hours.  For what it's worth, my Edge 530 had an estimated capacity of 24.73 hours on the same ride.

    All somewhat one-off data points.  Many from 2.10 SW, some may have been 3.04 beta.  From two different watches so nothing really conclusive I guess.  The one swim looks really weird, not sure what happened there.  Maybe I'll see if I can repeat it on a future swim.

    Edits:

    • Add LTE status for triathlon and fix swapped tags for the 90 min run and 90 min indoor spin (they we’re backwards)
    • I generally do not use Music so none of the above are while playing music
    • Added long outdoor bike ride
  • 0 over 3 years ago in reply to nord0296

    thanks for sharing your experiences, . some of those numbers are really low. was your triatholon with LTE enabled?  i'm usually not one to live on the bleeding edge with betas, but i may dive in at some point. my replacement 945LTE came last night so i am just setting it up and want to see how works with FW2.10 before i consider the beta. at the very least, the buttons on this 2nd watch have more reliable tactile feedback. i don't expect its battery performance, however to be that different from the first watch, but we will see.

  • 0 over 3 years ago in reply to derek87

    Yes, the triathlon had LTE enabled and in use.  I have not done any activities with the “Low Power Mode” LTE yet (reduced update rate to save battery)

  • 0 over 3 years ago in reply to nord0296

    interesting. i can't recall what DC Rainmaker said the spec was for LTE+GPS but no music...

    also, are you using GLONASS or Galileo?

  • 0 over 3 years ago in reply to derek87

    I think he noted 10-14 hours w/o Music (but with LTE), but could be mistaken there...

    I'm using default settings for GPS, I think - which seem to be GPS + GLONASS.

  • 0 over 3 years ago in reply to nord0296

    good to know. you are right, the default on the watch from the factory is GPS + GLONASS. at least with my 935, i never saw any notable difference in performance at least in my usage. so I've opted to use plain GPS to save myself 20% (roughly) in battery usage.

  • 0 over 3 years ago

    so, some updates. i'm on my 2nd 945LTE which i've had a a week to get some idea of how it is performing (first one was replaced due to horrible buttons...this one is much better).

    for this watch, i'm estimating a 8-9%/day in smart watch mode for the same watch face that was 6%/day on my 935.

    on the other hand, with a few more hours of GPS activities experienced, i think i'm getting close to a 3%/hr burn rate with vanilla GPS (no GLONASS, or Galileo), 1 sec recording.

    Aside, just like my 935: it goes quickly down from 100 -> 96% and then it slows up appreciably. this is even after leaving it on the charger for an hour after hitting 100%.

  • 0 over 3 years ago in reply to derek87

    I am contemplating using my 945 LTE for a 100 miler with a 30 hour cutoff but I am worried. I ran a 50 mile race in some mountains (so connection was a bit of a challenge). LTE off and no music but it was connected to my phone. After about 14:40 hours it had 51% battery left which leads me to believe it will last about 29-30 hours. A little disappointing. 

  • 0 over 3 years ago in reply to brentmreilly

    in my experience using plain GPS (not GLONASS or Galileo), this is one area where the 945LTE seems to be on spec. i am getting a burn rate of slightly less than 3% per hour both cycling, running, hiking. but i am not connected to buy phone so that perhaps makes difference. 

    if i were you, i would run a test if you can and leave your watch outside and running with no phone connected and see what your burn rate looks like.

  • 0 over 3 years ago in reply to derek87

    I do have a Fenix 6X Solar which will handle the race no problem. You think I should just wear that one?  I do like the look and feel of the 945 though