How a PDA Uses Power

First off, on all models of the JLT system, the PDA uses electricity even when it's asleep.  They all keep the operating system, programs, documents, and settings in RAM memory, which allows the PDA to be able to wake up and be usable instantly without needing to boot up, but RAM needs a small, constant amount of juice to remember what's stored in it (the RAM is also called the "main memory").  All versions of the JLT system can maintain the RAM in sleep mode for 10-20 days on a full battery charge.  With the hx4700, X30 and X50V systems based on the WM2003SE operating system, when the battery does completely die, everything in RAM is lost (the memory cards are unaffected, though)--when you plug it in again, it'll think it's right out of the factory, and you'll have to set up the OS and restore the system files, programs, and settings from the last backup--all that takes only about four minutes so it's not a huge disaster, just an inconvenience.  On the X50V with WM6 OS and on the X51V, though, everything in the RAM is mirrored on internal flash memory, so even if battery power goes out completely, all the settings, programs, etc. are saved.  When you charge the Axim again and turn it on, it'll take about 30 seconds to boot up, but then it'll be ready to use--you won't have set anything up again (except for setting the clock). 

Facts about the Battery

Li-ion batteries don't like to be discharged to very low levels often.  The lower the charge level, the higher the initial current (and thus heat) when you recharge them.  Heat causes damage to the electrolyte, lessening the amount of charge it can hold.  It's a basic function of the battery chemistry.  The battery itself contains a circuit to limit the charge/discharge current to prevent it from degrading too quickly (and to prevent any fire hazard), so if the battery drains once in a great while, the damage is minimal--if it happens only a couple of times a year, you'll never notice the cumulative damage.  The PDA also shuts down automatically when the battery drops to about 20% of capacity to keep it from getting too low--this also leaves the PDA with enough power to maintain the RAM for a few days, keeping you from losing any important data.  Still, if you frequently drain it all the way to the cutoff or very low, over a year or two you'll notice that the battery charges more quickly but that a full charge doensn't last as long as it used to--you may want to replace the battery after only a couple of years (still, since you can get a new battery for US$20 or less with shipping, there's no reason to refrain from using the full battery capacity every day if that's what you need). 

Also, Li-ion batteries lose some capacity if constantly kept at or near full charge most of the time over long periods.  The way the vast majority of customers use their JLT systems, though, that's unlikely to be a significant concern for many users. 

The other thing Li-ion batteries don't like is to lie dead for months or years.   Ideally, if you're storing a battery for years, you should charge it up completely and let it die completely once or twice a year to keep it in top shape for when you eventually need it. 


  1. Charge your PDA every night if possible when using the PDA normally.  If it's only drained a bit, then whether one charges it every night or every third night doesn't make much difference, but it's a good habit to be in--that way you'll never fire up your JLT PDA at the start of a busy day and find you've only got 40% battery capacity to start with.  The absolutely ideal thing is to charge it until the charging light shows a full charge, usually about three hours, then take it off the charger, but if it's more convenient to simply put it on the charger when you go to bed and take it off as you grab it on the way out the door in the morning, doing it that way won't be doing any great harm--even keeping the PDA on the charger for days at a time or even weeks at a time occasionally won't hurt much.   The PDAs and batteries are pretty resilient.  The other recommendations below will ensure the longest possible battery life, both in terms of how many hours of use you'll get out of each charge and in terms of how many years the battery will last, but if you do things differently a few times, you really won't notice any negative effects.  So other than charging your PDA nightly if possible, my biggest advice is, "Don't sweat it."
  2. If using the PDA sparingly, charge the PDA twice a week.  Keeping the charge level constantly above 90%, rarely letting it get below this, will reduce battery capacity by 10%-20% over the course of a year or two.  Most users use the PDA enough every day not to have to worry about this (and the daily charging convenience of always having a decent charge on the Axim and no danger of running out of juice outweighs the very minor capacity loss for users on the margin--those who aren't sure if they're using the PDA normally or sparingly: the "don't sweat it" principle), but if you leave Japan or your language course ends and you find you don't use your JLT PDA much any more, then keep an eye on the battery level when you do use it and let it drop to 60% or so before recharging it--twice a week  is probably a good schedule, but even once a week is OK if you rarely use the PDA.
  3. If you have an extra battery, chances are you rarely need it.  But a good habit is to swap it with the battery in the PDA every month or so.  That minimizes the number of charge/drain cycles on each battery and prevents the minor stress caused on one battery by having it lie around unused for months or years or keeping it fully charged all the time.  Note though that one shouldn't just keep swapping in a fully charged battery without also putting the PDA itself on the charger once in a while--the hx4700, X30, and X50V each contains a tiny rechargeable backup battery, which maintains the RAM for a few minutes while the main battery is being changed (the X51V doesn't, as it backups up the RAM to internal flash instead).  If the backup doesn't get recharged every so often, then it'll run out of juice after several main battery changes and then the iPAQ, X30, or X50V with WM2003SE OS will hard reset when the main battery is removed for a change, which is a pain (X50Vs with WM6 OS and all X51Vs will just lose the time and date).
  4. If you buy a new battery for your PDA, it'll likely have sat around for months before it got to you, so it won't hold a full charge at first (maybe only 80% or so)--it'll take many cycles of normal use before it gives you the long battery life it should.  To bring it up to speed more quickly, charge it up, then let it run down all the way until the PDA automatically shuts itself off (change the power and backlight settings so it doesn't turn off the light and put itself to sleep after a few minutes of inactivity).  Then do it again, and again.  After 3 cycles of this, it should be pretty much at full capacity--it may gain a few more minutes of capacity over the next month of normal use. 
  5. If you'll be storing the PDA unused for less than three weeks
    1. iPAQ, X30, X50V: just leave it on the charger for convenience.  If you do this often, though, then follow the "longer than three weeks" instructions below.  Doing it just a couple of times a year won't make much difference.
    2. X51V: Charge it up fully, then use the full power off function (hold the power button down until you get a message asking if you really want to fully power off the Axim).
    3. Extra battery: just charge it up before you go.  Any extra battery not in the PDA will hold its charge for several months.
  6. If you'll be storing it for longer than three weeks:
    1. iPAQ hx4700, X30, X50V: Charge it up fully, make a fresh backup file (using Data Backup on the Axims or iPAQ Backup on the iPAQ hx4700), then leave it off the charger.  The battery will die after 10-14 days or so, but if you don't do this often, it won't make a noticeable dent in battery capacity.  Except for the X50V running the WM6 operating system (most X50V users have the WM2003SE OS), you'll have to set up the OS and restore the JLT setup from the backup file when you start the PDA again (takes only about 4 minutes).  The X50V with WM6 should save a copy of the RAM to the internal flash memory before it dies, so when you start it up again it should set itself up automatically and be ready to use in about 30 seconds--all you'll have to do is reset the clock.   If you leave the PDA unused for more than 6 months, the advice above (3) for new batteries applies. 
    2. X51V: Charge it up fully, then fully power it off.  In full power off mode, rather than just sleep mode, the battery may last as long as a couple of months, as all it has to power is the clock.  When you get back, charge it up and push the power button; it'll take about 30 seconds to boot up, then it'll be ready to use, just as you left it.  If you've been gone long enough for the battery to die completely, you'll need to reset the clock.     If you leave the PDA unused for more than a year, the advice above for new batteries (3) applies. 
    3. Extra battery: just charge it up before you go.  Any extra battery not in the PDA will hold its charge for several months.

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