Battery: reading vs sleep vs shut down

[jlemonde]

Has someone made tests about the battery retention in these three cases?
(I am especially interested in such an experiment for the Kobo Clara HD)

For now, I'm used to let my device enter suspend mode after 5 minutes and shut down after half an hour -- and I've got battery for over a week or two, depending on how much I read --, but for this reason I have to start my device again several times a day.

I would like to know if the battery retention would be drastically lower if I disabled the automatic shut down and let it on all week.

I would also like to know if it uses more battery to stay in the reading mode instead of entering the suspend mode, if back-lighting is disabled anyway (I don't use it a lot). (In other words, is the suspend mode only about disabling the back-lighting?)

Have experiments be done? If not, what do you think? Thanks in advance!


Further questions asked in the replies :

Do you know if it is actually possible, maybe from the eReader.config file, to set the automatic shutdown to a few days? I know the setting is made there, but is it safe to try to put there any value, such as the number of minutes in a day and a half? I don't know if it only accepts given values or if it recognises any number...

[davidfor]

The short answer: Set the power off to never. You will be happier and you probably won't notice the difference in battery runtime

I have done most of those experiments over the years. Not with the Clara HD, but with one of my Kobo devices. The short answers are:

If the device is awake, it will use more power than if it is sleeping. It is noticeably more.

If you are actually reading (turning pages) it uses more power than if the device is just sitting there awake.

The faster you turn pages, the more power is used. And if you really want to chew through the battery, page through the library.


Having said that:

In all the years I have been using a Kobo ereader, I have always had the sleep set to 15 minutes and the power-off to never. How long this would last me is very hard to estimate. I tend to plug in daily for a least a few minutes. But, the last time I really tried, I worked out I was going to get two or three weeks with my Touch when I was reading about two hours each day. That was estimated by not connecting the device for a week and seeing that I had used about one third of the battery.

With my new Clara HD, I seem to be getting about 3% battery usage overnight. That is, from the time I disconnect from the PC until I look at the battery usage during my commute in the morning, it uses about 3% battery. During this time, there will be at least one hour of reading, the light is on, WiFi is enabled, the nightly automatic sync will have taken place and an elapsed time of about 8 hours (yes, I should sleep more).

Overall, I don't think the power saving of turning these devices off is enough to make up for the inconvenience of waiting for it to start up. And I don't think plugging in every couple of days is particularly inconvenient.

[jcn363]

Any machine use much more power to turn on/off than to maintain. Then the ideal situation will be: automatic shutdown disabled; automatic suspend mode disabled. The point is when you are reading and Morpheus appear, or when your brain goes on leaving behind a forgotten book. In this case (mine) the better is to set automatic shutdown disabled; automatic suspend mode enabled.
Good luck.

[Mrs_Often]

Originally Posted by jcn363

The point is when you are reading and Morpheus appear, or when your brain goes on leaving behind a forgotten book.

Haha

[jlemonde]

Thank you for your replies! I'm going to try to disable the automatic shut down and see how it behaves

Do you know if it is actually possible, maybe from the eReader.config file, to set the automatic shutdown to a few days? I know the setting is made there, but is it safe to try to put there any value, such as the number of minutes in a day and a half? I don't know if it only accepts given values or if it recognises any number...

[NiLuJe]

Plus, the actual strain of the boot process may actually completely offset the very, very meager gains a shutdown might have netted you, especially if you essentially use your device every day.

That, and the boot time is just plain annoying, no matter how fast it is (try cold booting a Kindle, it's, err, quite the test of patience ;D).

Definitely on the "never ever shut it down" camp . It'll shut down on its own if it needs to (i.e.,: when it runs out of juice ;p).

[mathil]

Well I did my own, very unscientific tests with my old H2O years ago, and the results were that with my usage I had more battery life with the automatic suspend mode *and* shutdown both turned on (usually to 15min and 30min).
The automatic suspend mode is, IMO, a sensible thing for all users to have. The shutdown is useful for me as I don't pick up my ereader more than once or twice a day, but if you read frequently for shorter stretches of time, I would recommend having it switched off as it would probably use up energy rather than save it. Though now that I use mostly my Glo HD I might try switching it off and see how it goes...

[koboy]

isn't a shut down the best/only way for the database to update correctly/properly/100%

i always shut down and restart after sideloading a book/books.

best wishes koboy

[NiLuJe]

@mathil: The H2O (first of its name) (and possibly other Mark5 devices) is a special snowflake in that its CPU frequency scaling is completely bonkers, so it's kind of a terrible (and, most importantly, unreliable, since I couldn't find rhyme nor reason to its scaling behavior) benchmark to begin with .

@koboy: I'm sure @davidfor could expand on that, but, in short: no.

[Mrs_Often]

Originally Posted by jlemonde

Do you know if it is actually possible, maybe from the eReader.config file, to set the automatic shutdown to a few days? I know the setting is made there, but is it safe to try to put there any value, such as the number of minutes in a day and a half? I don't know if it only accepts given values or if it recognises any number...

Yes it's safe to try any number of minutes. And if you're lucky, some might work. I've successfully had my Glo (non HD) power off after 48 hours* (entered in minutes) under firmware 4.8.x, but that didn't work** in (much) earlier firmware versions. My Clara is a little more fussy with what number of minutes it will and won't listen to. 48 and 55 hours hasn't worked so far under 4.9. I'm now testing 50 hours.

*Weirdly, the first two power-offs occurred somewhere between 12 and 25 hours, apparently irregularly, and then without changing any settings the Glo suddenly waited 48 hours before powering off, consistently. As if it was learning to count to 2880 (48x60)

**'Not working' means it will power off, but sooner than I tell it to. I haven't figured out after how long it powers off or if it's the same amount of minutes every time, but it seems to power off after (lots) more than 12 hours (maybe more than 20 but I'm not sure, I haven't paid enough attention). In any case it's a lot longer sleep-without-power-off time than you get with the maximum of 4 hours if you use the patch.

[Barbara1955]

10 mins sleep/ Never shut down...

[davidfor]

Originally Posted by koboy

isn't a shut down the best/only way for the database to update correctly/properly/100%

i always shut down and restart after sideloading a book/books.

Originally Posted by NiLuJe

@koboy: I'm sure @davidfor could expand on that, but, in short: no.

I agree with you on that one completely. If everything is working fine, there is no advantage to shutting down after sideloading books. And if things are bad, then shutting down doesn't actually help update the database. If the firmware can't write to the database during the normal operation, then it can't during the shutdown and it will be reading bad data from the database no matter what.

The only times I recommend shutting down in relation to the database are:

- As a test of a corrupt database. Though I'm not really recommending it, more that some problems are hightlighted afterwards.

- After restoring a copy of the database. In this case, you need to shutdown so that the firmware can reread the database from scratch. Without this, you might undo the point of restoring it.

[NiLuJe]

Warning: avert your eyes if you have no idea how SQLite behaves internally in WAL mode .

And in case you were extremely curious and wondering what happens to WAL checkpoints when the device is mounted over USBMS: it behaves completely sanely: Nickel commits the checkpoints before switching to USBMS, so the DB is perfectly sane & up-to-date at that point (provided it was sane to begin with, and the switch to USBMS was successful, which it should be, unless you have some really nasty crap running in the background).

[ps67]

Never shut down, 15 mins sleep, but I use a sleep cover (I bought cover in order to protect, not for sleeping but is useful also for sleeping).

[drjd]

Nowadays I am using my Glo at nights only so I have enabled auto shutdown at 30 mins. I don't mind rebooting it once everyday. As I recharge the device from laptop only, I do it once in a week. With 1 - 1.1/2 hours reading everyday, my battery does not drain much and it never goes down 50% when I recharge it. Previously when I used the device several times daily, I had disabled the auto shutdown feature, and used the sleepcover. I do not see any considerable battery life difference pattern in both the methods.