Trendeca was used to test the electrical and thermal performance of the battery charging feature of a portable GPS device. As we can see from the data, a “constant current, then constant voltage” charging method is implemented. Interestingly, the circuit designers have chosen to limit the maximum voltage to 4.1V (as opposed to the more commonly used 4.2V). Though this choice sacrifices some battery capacity, it is likely this decision was made to extend the total number of charge/discharge cycles the battery can endure.
The thermal data indicates that the battery temperature rose a maximum of 6° C above ambient during charging. This is expected as some energy is lost as heat during the electrochemical process that stores electrical energy within the battery. We note that the external temperature of the wall charger rose a maximum of 10° C above ambient. Given that the product is rated for charging in a maximum ambient temperature of 35° C, we expect the wall charger exterior will not get hotter than 45° C, which complies with electrical safety requirements.
Trendeca was used to measure the battery voltage, current, and temperature while the GPS device operated until battery depletion. The data indicates that the firmware is turning the device off at roughly 3.52V. The GPS device requires approximately 1 Watt of power to function. We conclude the firmware is limiting the device to 3.52V so that the battery can always provide the required current, ensuring the user always experiences proper operation. Interestingly, the current data indicates there is a “high power” feature that is turned on regularly at 15 minute intervals. This higher current event is likely associated with the GPS receiver subsystem.