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Tile didn't start with replaceable batteries--they still don't use them in all their products. I don't know how AirTags will be in practice, but user-replaceabl

by pfranz 6y ago

Tile didn't start with replaceable batteries--they still don't use them in all their products. I don't know how AirTags will be in practice, but user-replaceable batteries haven't been great. I don't know if it's a technical restriction or not, but "low-battery" seems to be a time based warning and not based on battery charge. So I either get an alert when 1 year has passed on all of my devices at the same time, or they just suddenly die without warning. I could see why Apple might avoid this user experience. Hopefully, their implementation is better.

Kye 6y ago
Your choice is a reasonable timer or extra circuitry and logic for monitoring battery power that cuts the battery life.
- idiotsecant 6y ago
  low-cost, low-power battery monitoring is like pretty much the most solved problem ever.
  - zsmi 6y ago
    you forgot something, low-cost, low-power, low-accuracy battery monitoring is like pretty much the most solved problem ever. low-cost & low-power & high accuracy, not so much
    - idiotsecant 6y ago
      What do you mean? It's literally just a 2-axis lookup table with voltage on one axis and SOC on the other.
      - xondono 6y ago
        Except it isn’t, not with modern lithium based batteries. Now most devices use direct voltage, coloumb counting and battery impedance to keep track, and that’s with known batteries.
        Dylan16807 6y ago
        Even for lithium ion batteries, notoriously hard to track, that's only true for the middle 70-80% of the charging range. It's very easy to check it a lithium ion battery is almost empty, just wait for the voltage to drop below 3.6 or 3.5 and maybe adjust for temperature. For a CR2032 specifically, you get a nice smooth drop over at least the last third to quarter of its charge. There's no difficulty in detecting that.
      - rkangel 5y ago
        It sometimes looks like that in the lab, but in real life it doesn't work. Here are two of the MANY situations that result in incredibly misleading voltage readouts: My battery is 80% charged, and then I go outside where it is 10 degC colder. Suddenly my battery voltage drops by 200mV and my battery looks 20% charged My battery is 80% charged and then I start playing a video. The increased load drops the battery voltage and suddenly my battery looks 20% charged.
  - kbos87 5y ago
    The fact that the Nest motion sensors / path lights in my home have been functioning for almost 2 years (their stated lifespan) without me needing to replace their tiny batteries boggles my mind.
habibur 6y ago
> I don't know if it's a technical restriction or not More likely because CR batteries don't drop voltage significantly as it discharges. And at full discharge it suddenly drops dead. Which is why it's harder to measure "remaining charge", as that's generally calculated on battery voltage.
- deleted 6y ago
  [deleted]
- rkangel 5y ago
  It's equally hard to get any useful information about Li-On or Li-Po based just on battery voltage which is why any actually useful battery indicator involves a charge counter (informally known as a 'gas gauge'). The actual coulombs of charge are counted in and out and that gives a much better estimate.
yardie 6y ago
Lithium batteries are high output until they're not. Like the CR2032 battery in my car keyfob it's working until it's not. The drop from 3V to 1V is precipitously fast. Also, 1 year is extremely conservative. I normally get 3 years out of these batteries. An Airtag that's constantly being interrogated may run out faster than say a keyfob used 5x a day
- culturestate 6y ago
  Yeah, I'd expect these to last notably longer than a year for most people. The AirTags marketing page gives the measurement spec: > Battery life based on an everyday use of four play sound events and one Precision Finding event per day. That seems like exceptionally heavy usage to me.
floatingatoll 6y ago
If the airtag dies without warning, wouldn’t it alert the user that the tag is out of range, and so then they could replace the battery? (Presumably Apple has a UI flow for this.)

by pfranz 6y ago

Kye 6y ago

Your choice is a reasonable timer or extra circuitry and logic for monitoring battery power that cuts the battery life.

idiotsecant 6y ago
low-cost, low-power battery monitoring is like pretty much the most solved problem ever.
- zsmi 6y ago
  you forgot something, low-cost, low-power, low-accuracy battery monitoring is like pretty much the most solved problem ever. low-cost & low-power & high accuracy, not so much
  - idiotsecant 6y ago
    What do you mean? It's literally just a 2-axis lookup table with voltage on one axis and SOC on the other.
    - xondono 6y ago
      Except it isn’t, not with modern lithium based batteries. Now most devices use direct voltage, coloumb counting and battery impedance to keep track, and that’s with known batteries.
      - Dylan16807 6y ago
        Even for lithium ion batteries, notoriously hard to track, that's only true for the middle 70-80% of the charging range. It's very easy to check it a lithium ion battery is almost empty, just wait for the voltage to drop below 3.6 or 3.5 and maybe adjust for temperature. For a CR2032 specifically, you get a nice smooth drop over at least the last third to quarter of its charge. There's no difficulty in detecting that.
    - rkangel 5y ago
      It sometimes looks like that in the lab, but in real life it doesn't work. Here are two of the MANY situations that result in incredibly misleading voltage readouts: My battery is 80% charged, and then I go outside where it is 10 degC colder. Suddenly my battery voltage drops by 200mV and my battery looks 20% charged My battery is 80% charged and then I start playing a video. The increased load drops the battery voltage and suddenly my battery looks 20% charged.
- kbos87 5y ago
  The fact that the Nest motion sensors / path lights in my home have been functioning for almost 2 years (their stated lifespan) without me needing to replace their tiny batteries boggles my mind.

habibur 6y ago

> I don't know if it's a technical restriction or not More likely because CR batteries don't drop voltage significantly as it discharges. And at full discharge it suddenly drops dead. Which is why it's harder to measure "remaining charge", as that's generally calculated on battery voltage.

deleted 6y ago
[deleted]
rkangel 5y ago
It's equally hard to get any useful information about Li-On or Li-Po based just on battery voltage which is why any actually useful battery indicator involves a charge counter (informally known as a 'gas gauge'). The actual coulombs of charge are counted in and out and that gives a much better estimate.

yardie 6y ago

Lithium batteries are high output until they're not. Like the CR2032 battery in my car keyfob it's working until it's not. The drop from 3V to 1V is precipitously fast. Also, 1 year is extremely conservative. I normally get 3 years out of these batteries. An Airtag that's constantly being interrogated may run out faster than say a keyfob used 5x a day

culturestate 6y ago
Yeah, I'd expect these to last notably longer than a year for most people. The AirTags marketing page gives the measurement spec: > Battery life based on an everyday use of four play sound events and one Precision Finding event per day. That seems like exceptionally heavy usage to me.

floatingatoll 6y ago

If the airtag dies without warning, wouldn’t it alert the user that the tag is out of range, and so then they could replace the battery? (Presumably Apple has a UI flow for this.)