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Old 11-26-2008, 11:25 PM   #1
horseflesh
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Fix for poor battery life on PRS-500?

I've had a 500 for almost 2 years now, and it's always gotten about 1000 page turns before the battery dies. The battery will also self-discharge if I let the unit sit for a week or so. From what I have read, this is a lot worse than I should be seeing. (If I only knew that when I got it, I would have gone for a warranty fix...)

I am not using any MP3s, but there is a Memory Stick in it for book storage.

Any ideas on how to improve things? Thanks in advance...
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Old 11-27-2008, 12:26 AM   #2
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None that I know about officially. Unlike the older generation of batteries that had a memory, the ones used in the Sony Reader should not have a memory.

Some time ago I thought that I was having a problem with the battery not keeping a charge as long as it did when it was new. I remembered that when I first had the unit I would always use the AC charger and later I would just recharge on the USB connection. I recharged on the AC unit a few times and the problem seemed to vanish. Either it cured itself or I started to kid myself. Either way, I will now use the AC charger every so often and fill in with the USB charging when I load and unload books.

There is a certain amount of battery drain when you use a Memory Stick (in theory less drain than an SD card) but not so much as your unit seems to be experiencing.

If you are not already using the AC charger for the unit, try it, it just might work.

Good luck and welcome to MobileRead.
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Old 11-27-2008, 12:49 AM   #3
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I've always used the AC charger, but I'm going to poke the reset button and put it on for a good long time and cross my fingers... I also pulled the memory stick since all my books currently fit into the internal memory. No reason to keep an empty stick in there draining some of the juice.

Thanks!

(Edit: one interesting thing that I noticed but forgot to mention in the first post... I had read about 300 pages, and dropped to 3/4 bars. Then for some reason I wanted to back up a bit in the book, and I clicked the back button a bunch of times--maybe 15-20? When it caught up to the inputs, the battery was down to 1/4 bars! Anyway, fingers crossed for a reset and recharge helping.)

Last edited by horseflesh; 11-27-2008 at 12:52 AM.
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Old 11-27-2008, 08:58 AM   #4
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A two year old PRS-500 is certainly going to have lost some of its battery capacity, compared with them it was new. Lithium Ion batteries, such as are used in the PRS-500, have a typical lifetime of about 5 years; one might expect a 2 year old battery to have lost 20-30% of its capacity, no matter how well it's looked after.

Unfortunately the lack of a user-replaceable battery is, I think, something of a weakness in the Sony eBook Reader range; most other manufacturers have - sensibly, IMHO - opted for batteries accessible to the user.
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Old 11-27-2008, 10:25 AM   #5
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One of your problem was definitely the memory stick.
Read this how to preserve battery capacity for Lithium-ion batteries.
http://en.wikipedia.org/wiki/Lithium-ion_battery

DO NOT DISCHARGE OFTEN! This is one of the golden rules.
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Old 11-27-2008, 11:27 AM   #6
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Quote:
Originally Posted by BlackVoid View Post
One of your problem was definitely the memory stick.
Read this how to preserve battery capacity for Lithium-ion batteries.
http://en.wikipedia.org/wiki/Lithium-ion_battery

DO NOT DISCHARGE OFTEN! This is one of the golden rules.
There seems to be considerable disagreement amongst the "experts" as to whether or not this actually is a "golden rule". Many sites inform one that frequent "top-ups" do no harm at all to a LiIon battery, while others say it should be avoided.

No matter what you do, though, the fact is that your battery is going to lose capacity with time; the best you can hope to do is to slow the process down.
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Old 11-27-2008, 02:50 PM   #7
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The battery isn't a spring chicken any more, but I never got over 2000 pages off a charge, even when it was new.

I did a hard reset and pulled the memory stick, the next few days will tell the tale I guess. I may have just had a crappy battery to start with.

Do file formats correlate to battery drain? All of the things I have read have been LRFs converted by BBeB or Caliber. (Can you just put raw PDF/RTF/TXT on the memory card? After having this thing forever I just saw a reference to that the other day.)
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Old 11-28-2008, 07:17 AM   #8
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Just replace the battery, it is fairly easy to do (I've done 3 now): http://www.mobileread.com/forums/sho...?t=8426&page=4
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Old 11-28-2008, 02:58 PM   #9
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That's great info, thanks.
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Old 11-29-2008, 04:57 AM   #10
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Just replace the battery, it is fairly easy to do (I've done 3 now): http://www.mobileread.com/forums/sho...?t=8426&page=4
Not so easy for those of us who find wiring a plug to be a technical challenge . I think I prefer to buy devices which are designed to allow the user to replace the battery.

It's interesting to note that new EU laws actually REQUIRE batteries to be replaceable for new devices. Not for the benefit of the consumer, but so that batteries can be removed and properly disposed of to avoid environmental issues. I would hazzard a guess that this might be a block on the PRS-700 being sold in the EU, since it was released after this new law came into effect.
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Old 11-29-2008, 08:15 PM   #11
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Harry is wise.

I agree with what he says about 20-30% capacity loss in 1-2 years.

I also agree that superstitious rules about do or don't discharge or top off are irrelevant with today's LiIon/LiPo batteries. The only real rule is that if you're going to store ot for some number of months, you'll minimize the aging and retain maximum capacity if you store it at half-charge. But in my experience, you can discharge it a little or a lot and recharge as many times as you want.

That being said, my experience with the PRS-500 is that its power management capabilities are poor compared to most other LiIon-powered devices I have. In fact, I've had my PRS-505 for a couple of months now and it's performed better with regard to the battery than the PRS-500 did even when new.

The PRS-500 only lasted about 3 weeks when new, regardless of the page-turns (I can only read about 200 pgs in a week what with work and family). Then it degraded to 1 1/2-2 weeks regardless of page turns after about a year. I blew my extended service plan on getting a replacement -- it was a refurb which was no better than my 1-yr degraded original unit.

The PRS-505, on the other hand, lasts over 4 weeks with few page turns. Granted, it's new, and we'll have to see how it works after a year, but it's starting out a lot better.
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Old 11-30-2008, 06:35 AM   #12
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Not quite sure if this has been asked before, but --

Since it is just a two-wire battery (no 'smart' leads/contacts) could you not just swap it with something of equal voltage (possibly higher mA for longevity) so long as it fit in the restricted space? Li-Ion, of course. Also -- leads being attached and whatnot.
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Old 12-01-2008, 01:06 PM   #13
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Since it is just a two-wire battery (no 'smart' leads/contacts) could you not just swap it with something of equal voltage (possibly higher mA for longevity) so long as it fit in the restricted space? Li-Ion, of course. Also -- leads being attached and whatnot.
In theory, yes, though I take no responsibility for any damage or personal injury which may result from my advice.

FYI:

The biggest issue is to make sure any replacement cell has a "protection circuit" on it -- that it's not just a raw cell. I haven't looked at the PRS-505 battery in particular, but I've never seen a consumer device that hasn't had the protection circuit attached directly to the battery. It's a strip of a PCB usually spanning the width of the cell attached to one end and covered with the heat-shrink outer packaging. There are usually metal tabs that come off the cell, terminate on the PCB, go through the circuitry on the board, and terminate at the wire leads that go to the main appliance PCB.

The protection circuit PCB has a protection IC that comprises comparators and switching logic to switch [usually] off-chip MOSFET transistors. It monitors overvoltage, undervoltage, and overcurrent conditions on charging or discharging and cuts the cell off of the rest of the circuit if the settings are exceeded. Since LiIon (and to a much lesser extent, LiPo) cells are subject to thermal runaway on overcurrent conditions, the protection circuit protects you against burns and/or fire, as well as consequential damage to the appliance. It also protects the cell against over-charging or over-discharging.

Aside from the protection-circuit issues, the only other concern is that the charging circuitry on the PRS-505 PCB has enough power dissipation/current-handling ability for a potentially higher mAH cell you may install. Given the size constraints, you PROBABLY don't have anything to worry about, because the existing charging circuit is probably already overrated for the cell they have in there. I know a lot of LiIon charging ICs from all the major manufacturers, and in my experience it's hard to find one that handles less than 500-800mA, and the cell in the PRS-505 has got to be in the 300mAh range (charging max current is usually set to <= 1C).

But as I said before, please understand that the risk is and must be all yours. I'm making estimations based on what I've seen in the marketplace of products and ICs, and I don't know for sure. Therefore, I take no responsibility for any damage that may occur as a result or in the course of having listened to my advice!
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Old 12-01-2008, 04:49 PM   #14
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If you're willing to examine the schematics, they're available in PRS-505 service manual.
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Old 12-01-2008, 05:53 PM   #15
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Thanks for the documentation!

Well, it has a charging circuit blocked out as IC401 on pg. 14, which is spec'd out at SN412005RHLR (BQ24032) on pg. 27. I've worked with the TI BQ series of parts before (I've used their BQ24010 charger). Their selection guide specs out the BQ24030 series as linear chargers with an integrated power FET capable of handling max 1.5A at a max input voltage of 18V. The BQ24032 variant has a regulated Vout of 4.4V (I guess when A/C-adapter or USB power is applied) versus other regulated setpoints of other BQ2403x variants. The max current is the same across the family.

A glance at the data sheet shows these chargers have charging-current setpoints determined by pins ISET1 and ISET2. ISET2 just switches between max charge rate and min (USB) charge rate. ISET1 apparently controls the max charge rate, and the 2.2K resistor in their schematic would work out to a max charge rate of:

Ibat = Vset * Kset / Rset = 2.5V * 450 / 2.2K = about 500mA.

(Based on their datasheet: Vset = 2.5V nom., Kset = 450 nom. for high Ibat values.)

So regardless of the mAh capacity of the cell you put in, it'll charge at 500mA max under A/C power. No surprise there -- it's the max they can draw on a high-charging USB port.

The bottom line is, whatever you can fit in there will probably work, and I see no conceivable potential for overtaxing the electronics in the PRS-505; it's pre-regulated. However, if the mAh rating of the replacement cell is too low (<< 500mAh), you'll charge it at too-high a rate on A/C power and shorten its charge-cycle lifetime. If it's 500mAh or greater, it'll take longer to charge but will have more charge-cycles in its lifetime.

So far, it looks like my initial assumptions were held up. I don't really have the time to dig any deeper into it -- it's got a complicated switching arrangement for USB vs. A/C power and current demands of the load circuit, but from experience and a couple of lines in the datasheet, I believe Rset controls and limits the maximum charging current which is what concerns us.

If anyone wants to review my analysis you can find the BQ24032 datasheet and app notes on TI's product page (click here).

Please note: this advice is offered without warranty. I've made a good effort to consider the relevant issues and I've tried to outline the basis of my judgments. That notwithstanding, I must repeat: You must assume full risk for any replacements or modifications you perform and I cannot and do not assume any responsibility for damage or injury or any other negative outcomes resulting from reading my comments and/or advice.
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