Machines and Accessories
Subject: Battery Charging on early-production digital talking-book
The digital talking-book machine (DTBM) battery pack contains
nickel metal hydride (NiMH) cells. These cells have a characteristic
self-discharge as described in Machines and Accessories Report 10-2. The
nominal battery pack operating voltage is 7.2 volts. A voltage of less
than 6.2 volts indicates that the battery is almost completely discharged.
If the DTBM is left disconnected from AC power the battery will continue
During the evaluation of prelaunch players it was discovered that the DTBM
would not attempt to charge a severely depleted battery whose voltage had
dropped below 3 volts. The NLS Engineering Section devised a circuit enhancement that
the DTBM manufacturer implemented to correct this issue. Players with
serial numbers above DS1-0064602 and DA1-0024536 have the enhanced
circuit and will not exhibit this problem.
If a battery pack in a player having a lower serial number will not charge
because of depletion below 3 volts, the following procedure should be used to charge
1. Remove the depleted battery from the player and place it in a
second player with the enhanced circuit.
2. Plug the second player into AC power. A period of one to five
hours may be required before the battery voltage rises enough to trigger
regular fast charging.
3. Wait until charging is complete, which may be an additional two or
three hours once fast charging begins.
4. Return the fully charged battery pack to the original
5. With the fully charged battery in the original player, enter the
service mode by holding the "Tone down," "Sleep," and "RW" buttons while
pressing the "Power" button to turn on the player.
6. In this service mode press :RW" to move to the "battery" menu
option, then press "Play/Stop" to select it.
7. In the battery menu press "RW" twice to move to the "Replace with
a full battery" action option and press "Play/Stop" to execute.
8. Turn off the player to exit the service mode.
Note: The enhanced circuitry for recovering a severely depleted
battery is only available on players with serial numbers above
DS1-0064602 and DA1-0024536.
Players can remain plugged into AC power without any ill effects. Leaving
players plugged in will ensure the battery is charged and ready for use.
Players left unplugged for more than two or three months should be
connected to AC power for two to three hours to recharge.
For more information contact:
John A. Brown
Head, Engineering Section
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