Battery management while charging

[bertrik]

Ok, so I think everyone agrees that charging to less than 100% can be beneficial for battery life (number of cycles), but there is disagreement on the extent this actually makes a difference in practical use. If we were to add a feature to allow the user to make a choice, I wonder what we can offer.

As a practical implementation, there are several things we can influence w.r.t. charging, depending on the target:
* voltage levels for warning and power-off
* current for the constant current part of the charge (40% of the battery capacity for example)
* voltage for the constant voltage part of the charge (4.20V for example)
* cut-off current for the constant voltage part of the charge (10% of the CC-current for example)

IMO, users can keep an eye on discharge levels themselves, so we don't have to manage that in software.
In rockbox, what we could do is to offer options for the constant voltage part, again depending on target, like from 4.00V to 4.20V.
(*if* we do this, I'd like to keep things simple, and offer only 1 parameter to configure).

If we are to allow lower voltages, I guess there will also be users who want a higher voltages. I think we should forbid that though.

[AlexP]

I really really wouldn't want an option for this.  We have far too many already without adding such an esoteric one.  If there really is an advantage (which there doesn't seem to be in practical terms) then it should just be changed.

[blr_p]

FLACs on the Clip+ last almost 20 hours with a new battery, so you're closer to .05C.  You'll never get up to 0.2C on an MP3 player, they use far too little power to discharge that quickly.

yeah, i noticed getting up to 16 -17h (even with q8 compresion) in the some people's logs for the clip+ with FLACs. I was thrown by a thread i'd seen in ABI where the user was complaining of less than 7 hours run time with FLACs and it was in OF. He replaced the player and tried with RB but still got the same out of it. That thread did not really reach much of a conclusion.

I can't see any way to get close to a 0.2c load on the clip+, playing FLACS & doom at the same time ? heh, not exactly a normal scenario. It would take something unusal or a decode heavier than FLAC. To put it simply if a user is getting 5 hours doing whatever then they've got a 0.2c load. Its then that the vendors graphs apply ~400 cycles to 80% capacity.

So the question then is, does a lower load mean a longer number of cycles than a 0.2c load. I cannot find any data on that. Looking at some docs they talk about 2c, 1c, 0.2c and you can see the lower the load the more the cycles before the battery comes down to 80%. So presumably lower loads result in more cycles before 80%

But how many more is unclear to me.
Post Merge: October 29, 2012, 04:21:05 PM

I guess if you find more data, you could try and make a better argument. 

More research papers would help build the case, is there anyone here with an IEEE subscription ?

This paper looks interesting.

How Depth of Discharge Affects the Cycle Life of Lithium-Metal-Polymer Batteries
This paper appears in:
Telecommunications Energy Conference, 2006. INTELEC '06. 28th Annual International
Date of Conference: Sept. 2006
Author(s): T. Guena
P. Leblanc
Page(s): 1   - 8
Product Type: Conference Publications
Conference Location :  Providence, RI
E-ISBN :  1-4244-0431-2
Print ISBN: 1-4244-0430-4
INSPEC Accession Number: 9296660
Digital Object Identifier :  10.1109/INTLEC.2006.251641
Date of Current Version :   04 December 2006
Issue Date :   Sept. 2006


Post Merge: October 29, 2012, 04:27:53 PM

You have misinterpreted what I said again. The battery bench plugin works fine on ipodvideo, as you should've been able to figure out from me saying I battery bench it often But you can't run the battery benchmark *in the Apple firmware*, because obviously Rockbox isn't running, so the only way to measure battery life in the Apple firmware is to actually time it manually while listening to the device so you know when it cuts out, and I can't really be bothered (plus I don't use iTunes, so I don't have any music on the player in a form that the Apple firmware can read). This means I can't compare the battery runtime it gets now to the *quoted* runtime from the device's specs, because comparing Apple's quoted runtime to Rockbox's current runtime is not a fair comparison: Rockbox is significantly more power efficient on this device, and so it will always get more runtime than Apple's firmware for *any* given state of the battery. The device was used for years by a friend before I came into possession of it, and they never used Rockbox, so I don't have any battery bench results for it that aren't from when I got it halfway through its life.

ok, now its more clear. I was confused why you mentioned benchmarking in apple when you already had RB's run time plugin. Forget about apple and what they claim run time should be.

Now the question is, how did you find the battery life evolve over the years in RB with the logs you got.

[torne]

ok, now its more clear. I was confused why you mentioned benchmarking in apple when you already had RB's run time plugin. Forget about apple and what they claim run time should be.

Now the question is, how did you find the battery life evolve over the years in RB with the logs you got.

I already gave you some estimates of this earlier in the thread.

When I got it originally, the battery life in Rockbox was substantially *worse* than it is now, as that predates some significant power management improvements on ipodvideo. After most of the improvements were in about 2.5 years ago, I got about 22 hours of runtime. Currently I get about 20.5. There haven't been *major* power management changes in that time, but obviously the code is different.

[soap]

Just wanted to chime in that I've been abusing my iPod 5th gen battery since 8 hours runtime was the norm.  I have many (older) battery benches posted, both in Rockbox and with Apple firmware.  I've run my battery down to (uncalibrated!) zero scores of times and still get > 18H on MP3.

[[Saint]]

I might as well add my story too:

I have an iPod 4G (Color/Photo) with the original battery in that I treat like absolute dirt by the standards outlines in previous posts. I charge it whenever the hell I feel like it, run it down to zero with absolutely no regard, and regularly leave it on the charger for days on end.
I am at least the second owner of this device so the person(s) before me may very well have treated it worse than I do...let me reiterate that this is the same battery the device was produced with, and (unlike my other iPod Color/Photo) still has the original HDD in place. I can get ~18+ hours out of it with mp3 @320.

[blr_p]

I am at least the second owner of this device so the person(s) before me may very well have treated it worse than I do...let me reiterate that this is the same battery the device was produced with, and (unlike my other iPod Color/Photo) still has the original HDD in place. I can get ~18+ hours out of it with mp3 @320.

How old's the unit ?

[torne]

They stopped making the ipod photo in mid-2005, so at least seven years