The Lithium Ion battery packs used in the Psion Teklogix 753x series of devices are referred to as "smart batteries" because they contain a memory chip which stores information including a serial number and the current state and usage history of the individual battery. They are designed to provide maximum usable run time and life cycle with minimal operator intervention or required maintenance. Much of this information can be viewed through the Power Management control panel applet and remotely through Psion Teklogix map.RF network management software.
In order to ensure that the batteries report accurate data, and to provide continued optimal performance, the batteries track their usage and automatically request a "calibration" periodically as they are used, if needed. The calibration is performed by either the gang chargers or the combo-dock chargers. The calibration process consists of a full discharge, and then a full charge of the battery pack. During normal operations, batteries will keep track of the amount of mAh drawn with each use and write this information to a register in its memory. When this "Discharge Count Register" reaches 850 mAh (HU3000 1900 mAh 7535, CV3000 1900 mAh 7530; 1100 mAh for the CV3001 2400 mAh 7530 battery) the pack will increment the "cycle count register" and reset the "Discharge Count Register". When the cycle count reaches a multiple of 20 cycles, the pack may set it's calibrate flag (if needed) alerting the charger to calibrate the battery on its next insertion. Under "normal" use conditions (use the battery until it is fully drained, then put it in a charger) the batteries may never require a calibration from the chargers as the terminals calibrate the batteries during use.
Each of the chargers has one shared discharge circuit used to discharge a battery for calibration. Due to this shared discharge circuit, only one bay can be in a discharge state at a time. The reason for this design is to eliminate the need for a fan in the chargers which would be required if more discharge circuits were used. Fans in chargers have proven to be a likely point of failure historically. Also the need for the charger to calibrate the batteries should be rare outside of the initial "new battery" calibration.
For a charger to calibrate a battery pack, the battery must meet four criteria:
If a battery meeting these four criteria is inserted into the charger, and if no other bays are utilizing the discharge circuit, the battery will be calibrated and its calibrate flag reset.
When batteries are shipped from manufacturing, they will have a charge level of between 10% and 30% (federal regulations prohibit transport of lithium ion batteries at above 40% charge), and the calibrate flag is set (the batteries need to be calibrated). Batteries will lose approximately 1%-2% of their remaining charge each month that they are stored at room temperature. Additionally, batteries shipped during the colder months may arrive with an insufficient charge to power the devices, and their valid discharge flag reset (having experienced temperatures below 40°F (5°C) during transit).
The recommended practice with new batteries is to fully charge them before use. This initial charge will likely not calibrate all of the batteries for any one of the reasons listed above. As a result, the initial use of a battery may not accurately reflect expected run times (since they may not be calibrated). As the batteries are used and cycled through the charger, each battery will ultimately be calibrated and over the first several charge cycles, all batteries will be calibrated and should provide optimal runtimes (maximum performance will be seen after batteries have been through 4-5 cycles, an increase of approximately 5% over the initial full charge).
Because the 753x battery packs track their usage and have no "memory effect", no detrimental symptoms will be experienced by recharging a battery which has not been fully discharged. A low battery indicator window will be displayed when the battery level reaches approximately 9% remaining power (assuming the suspend threshold has been left at its default value). The devices will automatically go to a suspend state when the battery level reaches approximately 6.5 volts (7.75 volts for batteries on the 7530). This should be an adequate charge to maintain the contents of RAM until the battery can be swapped. The devices should always be suspended before the batteries are replaced in order to ensure that the contents of the RAM memory are not lost. Adjusting the suspend threshold of the Power Properties applet will cause the low battery warning and suspend threshold to be raised to a higher level, allowing the device to maintain the contents of RAM for a longer period before a cold boot will be called. Certain peripherals (e.g. scanner, imager, RFID reader) may cause the battery to fall below the suspend threshold when they are triggered if the battery level is low.
All lithium ion batteries by their nature "wear out" and need to be replaced after a large number of charge cycles. The 753x batteries should provide optimal performance through approximately 300 cycles and will gradually degrade runtimes after this point until at approximately 500 cycles, run times will be reduced by approximately 30%.
Recommended practices for 753x battery use and maintenance: