Re-calibrating Prime's Battery?

[Jean-Baptiste Boric]

The NumWorks calculator has a similar battery management system. There's a self-contained Li-Ion battery charger chip to prevent over-charging, but the measured battery level is just the MCU's ADC running over a high-impedance voltage divisor. Unlike the HP Prime, the mechanism is extremely straightforward as the result (measured once every ~1/3 seconds) is directly projected onto 4 static battery levels and drawn on the status bar. Some people did notice a slight flickering right at the threshold, but the battery level indicator doesn't stand out and the screen's backlight is the main power consumer by far, so putting a hysteresis between battery levels wasn't a priority.

I believe most calculators share this architecture for power management since it's cheap and usually good enough. The downside is that it's quite imprecise, especially when current draw fluctuates quite a lot (which I assume the HP Prime G2 exhibits more than a calculator with a STM32F7).