Battery Profiling Checks Whether Capacity Claims Hold Up

Battery profiling is the difference between designing around a number printed on a cell and knowing what that cell can actually deliver in your circuit. In this clip from Elektor Lab Talk, Saad Imtiaz demonstrates how he uses a Qoitech Otii Ace to characterize batteries under representative active and sleep loads, then compares that approach with a Joulescope for power-consumption measurements. It follows the same practical problem Elektor examined in an earlier look at battery-powered embedded systems: nominal capacity alone does not tell you how long a real device will run.

Battery Profiling Under a Real Load

The current Qoitech Otii Ace Pro can act as both a power source and measurement instrument, while the optional Battery Toolbox adds battery profiling, testing, and emulation. Saad sets up a repeating duty cycle representing an embedded project, with a short wake period drawing the higher current and a much longer sleep period drawing far less. His example uses a 10 s wake interval and a 200 s sleep interval. The profiler then discharges the cell under that pattern and records how its voltage changes over time. That curve is more useful than a single capacity figure because the project may stop operating well before the cell is completely empty. In Saad's example, the system becomes unusable at about 3.2 V as the supply can no longer support the electronics properly.

When 3,000 mAh Turns Into 250 mAh

The most striking result came from 18650 lithium-ion cells sold or labeled as 3,000 mAh. Saad had already calculated the current consumption of his project but could not explain why its runtime was so poor. Battery profiling gave him the answer: some of the cells measured only about 250 mAh. The clip does not establish whether those cells were worn out, mislabeled, or simply poor quality, but it does show why checking capacity can save a lot of pointless debugging elsewhere in a design.

Saad also uses a Joulescope for detailed power measurements. In his setup, the target is powered from an external battery or supply while the Joulescope measures what the embedded system draws. The Otii arrangement can instead power the project directly while measuring it, which makes it convenient when the job includes both device power profiling and battery characterization.

Measure the Duty Cycle, Not Just the Label

For low-power embedded hardware, the useful question is rarely just "How many milliamp-hours does this battery claim?" A sensor node may spend almost all of its time asleep, wake briefly to sample or transmit, and then return to a very low-current state. Measuring those modes as a realistic cycle gives you a much better basis for comparing cells, estimating runtime, and spotting power-hungry firmware behavior. It also separates two problems that are easy to confuse: a project drawing too much current, and a battery delivering much less energy than expected.