rockbox/docs/BATTERY-FAQ

Q1: Are my batteries charged all the time when connected to my Player/Recorder?
A1: Player: the charging is all done by hardware and the exact
    functionality is hard to determine. It is however not recommended to keep
    the charger connected for more than 10-15 hours if you're not using the
    unit.

    Recorder: no. The charging algorithm is carefully crafted in to not wear
    out the batteries any more than necessary. If you're using your unit
    connected to the charger most of the time, use the 'deep discharge' option
    to save your batteries somewhat.

Q2: Will keeping my charger connected a long time damage my batteries? Can I
    leave it over night?
A2: There's a deep discharge mode and you can switch trickle charge on and off.
    If you use your AJB connected to the power supply the whole time, select
    "deep discharge on" and "trickle charge off". If you want to charge your
    AJB over night and take it with you the next day, select "deep discharge
    off" (that it starts charging immediately) and "trickle charge on"
    (that the batteries remain full).

    Trickle charge is needed to keep the batteries full. That's necessary because
    the device will stay powered on and continue to consume some power from
    the batteries (the hardware does not allow running from the charger
    without charging batteries, or powering off with the charger connected).
    The trickle charge time is 12 hours. It should be enough for you to disconnect
    your AJB in this time and turn it off / use it.
    However, after 12 hours of trickle charge, it will turn it off, the batteries
    are discharged and another charge cycle is started.
    
    As the Battery FAQ at http://www.greenbatteries.com/ puts it:
    "A NiMH battery can be charged and discharged hundreds of times,
    but whether that means 200 times or 800 times has a lot to do
    with how (you use it)".

Q3: Does Rockbox charge the batteries more/less/worse/better than the Archos
    firmware?
A3: Player: Rockbox doesn't affect the charging on Players, it is all done
    by hardware logic out of software control.

    Recorder: The whole algorithm is made to carefully charge the batteries full 
    and keep them full after that with a trickle charge option. Many documents 
    about charge ICs were considered. If you want to know details, then look 
    into docs/CHARGING_ALGORITHM. If you have comments, write to
    mail@uwe-freese.de or the Rockbox mailinglist.
    
    Test results with trickle charge (battery capacities measured with an
    external charger, Model "Conrad Electronic Charge Manager 2010", ~100 EUR):
    
    - after normal charge and top off time: 1798, 1834, 1819, 1815 mAh
    - after normal + top off + trickle charge (12h): 1784, 1748, 1738, 1752 mAh
    - charged with external charger: 1786, 1819, 1802, 1802 mAh

    You can see, whenever you take your AJB with you in the 12h trickle charge 
    period, the batteries are at least 97% full. :) 
    
Q4: What kind of batteries are there in my factory default Player/Recorder?
A4: Both ship with 1500 mAh NiMH (Nickel Metal Hydride) batteries.

Q5: Is it hard to change the batteries? Does it void my warranty?
A5: It is not very hard - the Archos manual and the FAQ on their web site
    describe how to do it. Their technical support confirmed that
    replacing the batteries with NiMH cells (of different capacities)
    will not void the warranty. Just don't remove the screws.
    
    Some units have been shipped with two sets of batteries, my Recorder 20
    only had one set. Someone actually had Archos send him new batteries
    free of charge after they had weared out, under the warranty.

Q6: How much do replacement batteries cost? Where can I buy them?
A6: http://www.greenbatteries.com sells 1800 mAh NiMH cells at $3.25USD each,
    and I bought 4 of the same GP batteries for 20 euros in an home
    electronics & household appliance store in Finland.  NiMH batteries are
    sold in almost all shops that sell consumer electronics, and in many
    online shops. Browse around. There's a pretty good comparison between
    different battery makes and models at the digital imaging resource site:
    http://www.imaging-resource.com/ACCS/BATTS/BATTS.HTM
    In Germany, www.reichelt.de sells GP 2000 batteries for 2,75 EUR (12/2002).

Q7: What kind of run-time can I expect on a set of fully-charged batteries
    when running Rockbox?
A7: For the stock 1500 mAh cells, from 6 hours to 8 hours, depending on
    which charger was used (see Q3) and the bitrate you use (higher bitrate
    means more harddisk runtime). It depends a lot on the condition of the 
    batteries. With 2000 mAh batteries, you should reach about 10 hours or more. 
    We are looking into implementing more battery-saving techniques in rockbox 
    to make it rock longer.
    If you have a modified AJB with 8 MB, you can reach playing times of up to
    16 hours with 2100 mAh batteries.

Q8: Can I use different batteries in my Archos? How much playtime would
    I gain by using 1800 mAh batteries instead of the 1500 mAh ones?
A8: Only use NiMH-type rechargeable batteries. It is considered to be safe
    to use NiMH batteries of different capacities though, a lot of people
    have purchaced 1700 or 1800 mAh batteries to replace the stock 1500 mAh
    cells and have the device run a bit longer. 2000 mAh batteries are
    just appearing in shops are equally good to use.
    
    In theory, running time = capacity of batteries / current drawn by device,
    so running time should increase linearly by the capacity, and 2000 mAh
    over 1500 mAh should give 33% longer running time. In practice, the
    mAh ratings are more or less tuned up by the marketing department
    (think of watts on the back of "hi-fi" speakers and amplifiers) and
    what you actually get out of the cells is something else than what is
    printed on them. Check the excellent imaging-resource link above for
    details!

Q9: Can I use non-chargeable batteries in my Archos?
A9: This is not recommended. The unit has been designed to operate with
    four 1.2V batteries producing about 4.8V at most, and using 1.5V
    alkaline/zinc carbon batteries will produce around 6.0V, which will
    heat up the unit a lot more and might even damage it. The Archos
    manual explicitly tells you not to do so.
    Also, if you connect the charger, it may even destroy both the batteries
    and the unit.

Q10: Can I use a different charger?
A10: The short answer is: Using a different charger will void your warranty
     and can be dangerous to your unit, so we can not recommend it.
     
     On the other hand, people have successfully used different chargers
     with similar specifications as the stock charger. The charger must
     have the same kind of connector with same polarity (center positive/+).
     The charger should supply at least 7-8 volts, and if it provides
     more than 10V, it probably should be regulated to 10V (do not
     directly plug it in your 12V car battery or it's charger!).
     The universal travel charger sold by Archos is specified at
     12V, 1.2A so that's probably the maximum rating you should use.
     A good circuit for powering from a car battery or other source
     with a higher voltage would be a 600 mA fuse and a 10V regulator like
     a 7810 of your favourite manufacturer in series.
     
     Inside the Jukebox there is a regulator which limits the charging
     current applied to the batteries. The higher the input voltage, the hotter
     this IC gets. Don't use an input voltage above 12V.
     Using lower charging voltage < 10V will slow down the charging. But the
     rockbox charging algorithm should work then, too.

     These are the output voltages of an original archos power supply:
     - connected to AJB Recorder, not charging: 13,7 Volt
     - connected to AJB Recorder, charging: going down to 10,4 Volt

     Here is how changing the input voltage changes the charging current:

      voltage   charging current (limited only by the AJB)
      ------------------------------------------------------
      7,0V          10 mA
      7,5V          30 mA
      8,0V          50 mA
      8,5V          70 mA
      9,0V         140 mA
      9,5V         250 mA
      10,0V        330 mA
      10,5V        350 mA
      11,0V        350 mA
      11,5V        350 mA
      12,0V        350 mA
     
     To summarize:

      - do not use an input voltage > 12V (it will only heat up the regulator)
      - optimal input voltage is 10V (regulated)
      - use a fuse of ~600mA
      - using a different charger voids your warrenty
     
     Many people are happy using an external quick charger which
     is specified to work with NiMH batteries. This is completely safe
     and will not void your warranty.

Q11: Can I buy a replacement charger exactly as the one Archos shipped?
A11: The FAQ on the Archos web site and the top of the charger both read:

      Output: 9VDC 600mA
      Center positive (+) polarity
     
     The universal travel charger sold separately on the Archos web site
     is specified for 12VDC, 1200mA output.
     
     Chargers with similar (or user-adjustable) properties are available
     at shops selling consumer electronics.

Q12: I often need to stop my player for about 15 minutes or so, and when I do
     it runs off it's batteries.  I was wondering, which is best: shutting the
     player down completely and rebooting it when I want to listen again, or 
     leaving the unit on?  Which way does it draw more power?
A12: In our testing we found the following results:
         HDD off, backlight off, idle 94 mA
         HDD off, backlight off, play 97 mA
         HDD off, backlight on, idle 129 mA
         HDD off, backlight on, play 131 mA
         HDD on, backlight on, play 230 mA
         HD on, reading, backlight off ~ 600 mA
         HD spin up before read max 800 mA

     Using the power draw measurements shown above, lets look at the numbers:
     Power-down and restart vs. paused for 15 minutes.:

     Pause for 15 minutes will draw: 94 mA / 60 minutes * 15 minutes =
     23.5 mAh.

     Power-down and restart will draw about (800mA / 3600 seconds * 3
     seconds = 0.6666 mAh) + (600 mA / 3600 seconds * 6 seconds = 1.0 mAh) +
     (230 mA / 3600 seconds * 8 seconds = 0.5111 mAh) = 2.18 mAh total used.

     Thus, leaving it paused for 15 minutes draws more power (23.5 mAh) than
     turning off and then on again (2.18 mAh).

     So where is the break-even point?

     Each second of pause will draw about 94 mAh / 3600 seconds = 26 <20>Ah.

     2.18 mAh / 26 <20>Ah = 2180 <20>Ah / 26 <20>Ah = 83.5 seconds

     Thus a shutdown and restart uses as much power as 83.5 seconds of pause.

Q13: When I plug in the charger when the Recorder is turned off, it turns
     itself on and starts charging in the Archos software? What's up?
A13: There is a switch in the DC IN jack of the Jukebox - when a charger (or
     whatever) is plugged in, the unit is powered on, even if the charger
     is not plugged in a mains outlet.
     
     If the charger is providing power at this point, the Archos firmware
     located on the FLASH ROM does not load a new firmware version (like
     Rockbox) from the disk, but goes into charging mode instead. You can
     use this feature to get to the Archos charger if you want to.

Q14: When I plug the charger in my Recorder, it doesn't immediately start
     charging the batteries!
A14: When Rockbox is running on the Recorder (the device has been booted
     without the charger) it's power management code runs once per minute
     (thus the charge level and charging status is only updated every minute).
     If the battery is not full, it will start charging. If the 'deep
     discharge' mode is enabled in the settings menu, it will start charging
     only when the battery is almost empty.

Q15: What about the memory effect? Should I be worried about it or not?
A15: That depends on who you ask. ;-) NiMH sellers say NiMHs are better and
     do not have a memory effect, but the usual opinion seems to be that
     they do, although it is very small.
     
     However, if you use your AJB connected to the charger all the time,
     we recommend you to use the deep discharge option.

Q16: When I start my Jukebox, (dis)connect the charger and browse through the 
     directories, the battery level changes a little bit. Sometimes it's even 
     going up without the charger is connected! What's wrong?
A16: Nothing's wrong. The battery level is calculated out of the voltage. 
     Because disk spinning, LED backlight, charger all influence the actual 
     battery voltage, it is usual that the battery level is going a little bit 
     up and down sometimes. This cannot be avoided although we tried to make the 
     battery level display as little confusing as we could.

Q17: My batteries are at 92%, the charger is connected to my recorder, deep
     discharge is off. But charging doesn't start. What's wrong?
A17: Charging starts if the battery level is below 85%. This is because
     charging batteries that *are* already more or less full is not good for
     the batteries and the end of the charging cycle can't be detected safely.
     So it's better to start at a level at least as low as 85%.
     If you want to have full batteries in the morning, leave the charger
     connected over night. Charging will then start some hours later. The
     second possibility: Use the Archos charging algorithm. At least,
     your batteries will be full one more time. ;-)