Battery Percentage

[NishchalSrinarayanan]

How do I get the hub's battery percentage? I have a spike prime hub.

[dlech]

Can you tell us more about the use case?

[NishchalSrinarayanan]

I would like to know the battery percentage so I can better understand and measure the robot’s power usage. I am participating in FLL, and I’ve noticed that the robot appears to use less power as the battery level decreases. Knowing the exact battery percentage would allow me to run and test the robot consistently at the same charge level and adjust my code accordingly.

[dlech]

There is already hub.battery.voltage(). Would that work for your use case?

The voltage can change depending on the load (e.g. how many motors are running). The battery doesn't really have a way to get an accurate charge level, which is why we haven't implemented that yet. But having the actual voltage available to use for feedback in a control loop is probably more useful anyway.

[NishchalSrinarayanan]

do you know how the spike prime application get's it's battery percentage?

[dlech]

No, I don't know how it does it. It could be just a direct scaling from voltage to percent. Or it could be doing additional processing of the voltage to account for the fact that voltage isn't really an accurate indicator of the amount of energy left in the battery.

[tyanekocom]

# import umath
from pybricks.hubs import PrimeHub
from pybricks.pupdevices import Motor, ColorSensor, UltrasonicSensor, ForceSensor
from pybricks.parameters import Axis, Button, Color, Direction, Port, Side, Stop
from pybricks.robotics import DriveBase
from pybricks.tools import wait, StopWatch, run_task, multitask

hub = PrimeHub()


voltage = hub.battery.voltage()

min_voltage = 6500
max_voltage = 8400


battery_percent = (voltage - min_voltage) * 100 / (max_voltage - min_voltage)
battery_percent = max(0, min(100, battery_percent))  # 0〜100% 

print(f"volt: {voltage} mV")
print(f"Battery level: {battery_percent:.1f}%")

I use it like this