Simplify Validating a Battery's Capacity and Energy for End-Use Loading Conditions

A key part of determining a mobile device’s battery run time is validating the battery’s capacity and energy under dynamic endues loading conditions.

Once you have validated a battery’s stated capacity and energy ratings based on data sheet conditions, you also need to validate them under dynamic loading conditions that reflect the actual end-use. Just as higher constant current discharge rates lead to reduced capacity and energy obtained from a battery, high peak pulsed dynamic discharge currents also yield lower capacity and energy compared to an equivalent constant current discharge having the same average value. The amount of peak pulsed discharge that can be tolerated is highly dependent on the battery’s design. Because of this, you must validate the capacity of the battery under consideration under dynamic loading conditions reflecting the actual end-use as part of optimizing the battery run time of a mobile wireless device.

Validating a battery’s capacity and energy for end-use loading conditions requires you to accurately log voltage and current while reliably recreating the dynamic end-user loading conditions.

Just as with static charging and discharging, small differences in dynamic loading conditions for discharging can lead to large differences in the capacity and energy obtained from the battery. Non-linear time-variant battery behaviors will yield different capacity and energy results, which are caused by differences in dynamic loading. Consequently, you need an accurate dynamic load profile for discharge. Using the actual mobile device provides the most realistic dynamic loading profile but has some drawbacks. Often it is difficult to reliably create the necessary conditions for the device to have it operate in the desired fashion, and usually there can be significant variance when doing this on a repeated basis. A solution for doing this on a repeatable basis is to capture the device’s dynamic current drain over an appropriate period and then play it back with an electronic load that will support this type of operation, to discharge the battery.