Archived 2013-12-08
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The charging circuit of the HP 100LX and 200LX provides 100mA for 6 hours, then it switches to trickle charging mode which only submits enough current for the batteries not to lose their charge again by self-discharging.

That means, the default mechanism is only capable to submit 600mAh of charge to rechargeable batteries.

In order to make sure modern rechargeables with capacities much beyond 600mAh are fully recharged, you can use a software program which modifies the charging mechanism. The current cannot be made higher via software, but the charging time can be extended.

Modern 2800mAh batteries need in theory 28 hours with 100mA in order to be charged fully when they were completely empty. This is quite a lot of time.

In order to allow for a longer charging time, you have several options:

  • Disconnect and reconnect the palmtop after less than 6 hours manually. This resets the charging circuit and begins a new period of 6 hours for charging. However, this is quite inconvenient (but could be automated using a timer).

  • If you have a palmtop with a Times2Tech doublespeed upgrade, make sure you have the latest Times2Tech doublespeed driver spd31.exe on your palmtop. Download it from here.
    The command line switch /N for spd31.exe sets constant full-rate chariging with no timeout.
    The command line switch /N- does the same, but starts off with batteries not charging.
    The driver comes with the utility CHRG.COM which allows to enable / disable charging.

    Please note that this driver should only be used if you have an original Times2Tech Doublespeed upgrade, not one of the other options provided by other companies (e.g. the 32MHz doublespeed upgrade by hermocom).

  • With another or no doublespeed upgrade, use this option:

    Use a stand-alone tool which replaces / manipulates the built-in charging mechanism. You get a list of such tools here.

Always keep in mind, that the palmtop recharges with 100mA. This lets you determine the time the palmtop should stay on AC power for the batteries to be fully charged (capacity in mAh / 100mA = charging hours) Use this calculation result for configuring the charging duration of the tool of your choice.

If you do it like I did, configuring the tool to charge infinitely with 100mA to make sure it always charges, if you connect the Palmtop to AC power, you must make sure that you do not forget the Palmtop on AC for too long. My usage pattern was to connect the Palmtop each night to AC and always(!) disconnect it in the morning, then using it for many hours over the day.

Even if the batteries are overcharged a bit, it does not do any harm. The batteries may fail a bit earlier, maybe not after three years but already after two years, but they don't cost much, so rather choose a convenient and power-safe setup than one which has the risk of data loss or an inoperable palmtop due to empty main batteries.

Also, to be even safer, you could simply always carry a pair of (non-rechargeable, because rechargeable batteries always have quite high self-discharging rates, except those called "Sanyo eneloop") with you for replacement. Make sure, however, to not let the palmtop recharge them when in use! Above mentioned software tools may enable charging even if you disable it in the HP's setup application. So if you have set up one of these tools, use non-rechargable batteries only without the AC adapter connected!

Recommendation:

Recently (2012/2013) more and more palmtop users recommend Sanyo "eneloop" cells for the palmtop, as they have a very low self-discharging rate.