BattMan, Battery life estimates on watchfaces | The Rebble Alliance | Page 1

untold parcel May 29, 2026, 9:45 PM

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Looking for testers for BattMan, a very simple watchface that estimates the remaining battery life time, and estimates the time to full charge while charging.

RePebble Store Link

Charge and Discharge rates are stored in persistent storage (as seconds-per-battery-percentage), and are re-calculated based on a first-order filter when there are consistent changes in battery percentage while the watchface is in focus. Only two integers are stored in persistent storage, and the calculations are only run when the battery level changes.

If you have a rectangular watch and are interested in testing this (how it compares to Muninn or the battery reporting in app), please let me know how accurate it gets.

If it works out, looking to release this as a simple .c/.h library for folks to use, with a simple callback for the battery event and a function to retrieve the estimated battery life or charge eta.

Pebble Appstore

BattMan - Pebble Appstore

Simple Watchface that predicts battery life and charge time. Weather from Open-Meteo.

Charge and Discharge rate estimates are saved to persistent storage, an

tough blaze May 29, 2026, 9:51 PM

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Count me in.

untold parcel May 29, 2026, 9:55 PM

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tough blaze Count me in.

Nice, thanks! What watch will you test it on? (Will take at least a charge cycle or 2 to get accurate numbers)

tough blaze May 29, 2026, 9:56 PM

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I'm currently running Muninn on Steel, Time, Time Steel, Round, and 2 Duo.

untold parcel May 29, 2026, 9:56 PM

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Dang, you got the whole fam

tough blaze May 29, 2026, 9:56 PM

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How will running Muninn and BattMan together work?

untold parcel May 29, 2026, 9:57 PM

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I'll try to make a version that works on the round.

tough blaze May 29, 2026, 9:57 PM

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My orders for Time 2 and Round 2 haven't arrived yet.

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I have a Pebble 2 (Diorite) coming in the mail.

untold parcel May 29, 2026, 9:58 PM

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tough blaze How will running Muninn and BattMan together work?

BattMan does not use background workers or wake events. It only collects data passively while it's in the foreground (the watchface is visible on the screen). Should not be an issue running Muninn at the same time.

tough blaze May 29, 2026, 9:58 PM

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I use them all for testing my watchfaces (Dual Time Zone and Field Day Info).

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So, you're saying that when another watchface is active, your code doesn't run at all?

untold parcel May 29, 2026, 9:59 PM

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tough blaze So, you're saying that when another watchface is active, your code doesn't run a...

Correct. Which is why it needs to be tested see if it works, then could be released as a library that other watch faces can import and use easily.

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(I currently don't own any watches)

tough blaze May 29, 2026, 10:00 PM

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So, if someone switches between watchfaces, how accurate would it be?

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You can pick up a Pebble Steel on FleaBay. It has a removable back, so it less difficult to do surgery on it to replace the battery and foam strip.

untold parcel May 29, 2026, 10:02 PM

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It will wait for consistent battery percentage changes (timing between falling/rising edges of the battery percentage) to get as accurate as it can be.

tough blaze May 29, 2026, 10:03 PM

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Actually, I have a New Old Stock (NOS) Pebble Steel in Black that I've put a new battery and foam strip in that I'm open to selling. I don't need two copies of the same watch.

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Pebble Steel is Aplite, which is the same innards as the original Pebble Classic.

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Should I start BattMan when the watch is fully charged, or does it matter?

untold parcel May 29, 2026, 10:11 PM

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Does not matter

tough blaze May 29, 2026, 10:12 PM

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If I were to incorporate your library into a watchface, I would only want the battery part. I hope the weather part is separate.

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I have BattMan running on PTS (Aplite) now...

untold parcel May 29, 2026, 10:14 PM

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tough blaze If I were to incorporate your library into a watchface, I would only want the ba...

Yes, it would just be a battery info lib

tough blaze May 29, 2026, 10:19 PM

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UI Suggestion: Since you only support monochrome, you shouldn't have separate choices for Background Color and Text Color. Half the permutations (Black/Black and White/White) are useless. Simply have two radio buttons for the themes: Light and Dark

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I am also running BattMan on Pebble Time Steel (Basalt)...

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I just verified BattMan won't install on Pebble Round (Chalk)...

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I'm now also running BattMan on Pebble 2 Duo (Flint).

untold parcel May 29, 2026, 10:35 PM

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tough blaze UI Suggestion: Since you only support monochrome, you shouldn't have separate ch...

It should support color (I used it in emulator on time and time 2), but I do agree the UX on monochrome can be improved.

Will re-arrange the elements to fit on Round and Gabbro later tonight.

Weather is from open-meteo, not related to the battery stuff at all.

Any other features/tweaks you want to make the testing go smoother?

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I'd also be interested in taking that Steel off your hands if you're up to it.

untold parcel May 29, 2026, 10:38 PM

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tough blaze I'm now also running BattMan on Pebble 2 Duo (Flint).

If you ever see the rate have "raw" beside it (instead of "avg"), it has just re-calculated the (dis)charge rate based on data it recorded.

tough blaze May 29, 2026, 10:55 PM

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I see "1h40m/% avg." It's not clear what this means.

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Take a look at the UI for the color settings in my watcfaces. It might inspire how you choose to do your color settings.

lethal bay May 29, 2026, 10:57 PM

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1h40m for 1% drop

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On average

tough blaze May 29, 2026, 10:57 PM

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Your UI should make that clear.

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Of course, if you have suggestions for improvements to my watchfaces, I'm all ears.

untold parcel May 29, 2026, 11:05 PM

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tough blaze Your UI should make that clear.

Taken. The UI is more of a minimum viable product: it's the algorithm that is under test.

tough blaze May 29, 2026, 11:45 PM

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Understood. However, I need to clearly understand what I'm testing.

untold parcel May 29, 2026, 11:48 PM

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Will make some changes and get a new 0.0.2 version out. Won't mess with any battery data it has already collected.

untold parcel May 30, 2026, 12:33 AM

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tough blaze Your UI should make that clear.

Released a 0.0.2 with your UX tweaks in mind:
when discharging: "--%, []d[]h left, []h[]m/1% drop"
when charging: "--%, full in []m[]s, []s/1% chrg"
Added support for Chalk
Added better UX for b/w watches (select color theme from settings, not independent bg and text colors)

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^chalk

tough blaze May 30, 2026, 12:49 AM

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Since you're supporting Chalk, might as well add Gabbro to the mix.

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Somehow, I can't get 0.0.2 to load. I only get 0.0.1.

untold parcel May 30, 2026, 1:05 AM

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tough blaze Since you're supporting Chalk, might as well add Gabbro to the mix.

Will do. Low on the priority, since hardly any hardware exists.

untold parcel May 30, 2026, 1:06 AM

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tough blaze Somehow, I can't get 0.0.2 to load. I only get 0.0.1.

Any errors?

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I think it just takes a while for the versions to propogate ot the phone appstore, while they show up instantly on the web appstore

untold parcel May 30, 2026, 1:38 AM

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Just released a 0.0.3 adding support for Gabbro, and limiting color options for background and text to avoid decision overwhelm.

tough blaze May 30, 2026, 2:36 AM

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Yeah, I just pushed updates to my watchfaces, and they aren't updating yet in my watches.

tough blaze May 30, 2026, 2:37 AM

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untold parcel Just released a 0.0.3 adding support for Gabbro, and limiting color options for ...

This looks much cleaner. It's easier to read.

tough blaze May 30, 2026, 3:31 AM

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Here's BattMan on multiple platforms. I think the centered information in the Pebble Round looks the best. I'd like to see it the same for the rectangular watches.

untold parcel May 30, 2026, 3:33 AM

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tough blaze Here's BattMan on multiple platforms. I think the centered information in the Pe...

Centered looks really nice!
Might have to make that change across all platforms...

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Instead of weather, what would you rather see on that bottom line?

tough blaze May 30, 2026, 3:36 AM

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Anything that's not battery related is inconsequential.

untold parcel May 30, 2026, 3:48 AM

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So be it.

untold parcel May 30, 2026, 1:38 PM

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tough blaze Here's BattMan on multiple platforms. I think the centered information in the Pe...

Mind if I use this image for the appstore banner?

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And if anyone has a PT2 and is willing to test this face out, we're still looking for testers. It does not use wake events or background workers, so the watchface has to be active for it to calculate drain and charge rates. BattMan on RePebble

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(And it won't interfere with Muninn. In fact, it'd be nice to run both to compare how accurate they are)

untold parcel May 30, 2026, 10:36 PM

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tough blaze Here's BattMan on multiple platforms. I think the centered information in the Pe...

Any of the watches say anything other than 1h40m/1%?

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Or while charging, something other than 60s/1% chrg?

tough blaze May 31, 2026, 2:16 AM

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The Time Steel shows: 1h5m/1% drop

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The Time shows: 1h11m/1% drop

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The 2 Duo shows: 1h40m/1% drop

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The Round has such a bad battery, it doesn't stay on for an entire day.

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I wore the Steel all day today while displaying a different watchface.

untold parcel May 31, 2026, 4:13 AM

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@tough blaze Nice, so the time steel and time have updated data, getting closer to accurate. Does your 2 duo have a 7 day battery life? Wonder what the charge rate shows while the round is plugged in?

tough blaze May 31, 2026, 4:28 AM

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The 2 duo lasts weeks on a battery.

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The Round shows: 60s/1%chg

tough blaze Jun 1, 2026, 3:46 PM

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3d5h left for 80% charge doesn't seem right to me. I'm not sure Muninn is correct either. It's a Pebble Time Steel with original battery.

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29h9m left for 50% charge seems rather pessimistic to me, even though it's a Pebble Time with original battery. I know the battery lasts longer. In this case, Muninn appears to be accurate at 3.3 Days left.

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6d8h left for 91% charge on a Pebble 2 Duo that's less than 5 months old seems pessimistic to me. Muninn appears accurate at 22 Days left.

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6d23h left on 70% charge actually may be accurate. It's a new battery in a Pebble Steel, and I updated my watchface to update once per minute instead of once per second. Muninn needs more samples to make estimates right now.

untold parcel Jun 2, 2026, 12:22 AM

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tough blaze 6d23h left on 70% charge actually may be accurate. It's a new battery in a Pebbl...

This is all very good feedback. Thank you for running these tests this weekend.
As I work on a new version with an updated algorithm, would you mind keeping the tests rolling?

tough blaze Jun 2, 2026, 12:35 AM

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Sure. No sweat, bud.

tough blaze Jun 2, 2026, 12:52 AM

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By the way, how often does your app refresh the screen?

untold parcel Jun 2, 2026, 2:31 AM

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tough blaze By the way, how often does your app refresh the screen?

I think it is set to once a minute plus when the battery level changes, but I will double-check.

untold parcel Jun 2, 2026, 3:36 AM

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Yes, once per minute, plus whenever the battery percentage changes (every 10% for Aplite-Diorite, every 1% for Emery, Flint, Gabbro)

#BattMan, Battery life estimates on watchfaces