Read system voltage on Pico W and estimate battery percentage

battery.py

full_battery = 4.2                  
empty_battery = 2.8  

def get_vsys():
    # Pico W voltage read function by darconeous on reddit: 
    # https://www.reddit.com/r/raspberrypipico/comments/xalach/comment/ipigfzu/
    conversion_factor = 3 * 3.3 / 65535
    import network
    from machine import Pin, ADC
    wlan = network.WLAN(network.STA_IF)
    wlan_active = wlan.active()

    try:
        # Don't use the WLAN chip for a moment.
        wlan.active(False)

        # Make sure pin 25 is high.
        Pin(25, mode=Pin.OUT, pull=Pin.PULL_DOWN).high()
        
        # Reconfigure pin 29 as an input.
        Pin(29, Pin.IN)
        
        vsys = ADC(29)
        return vsys.read_u16() * conversion_factor

    finally:
        # Restore the pin state and possibly reactivate WLAN
        Pin(29, Pin.ALT, pull=Pin.PULL_DOWN, alt=7)
        wlan.active(wlan_active)
        
voltage = get_vsys()

percentage = 100 * ((voltage - empty_battery) / (full_battery - empty_battery))
    
if percentage > 100:
    percentage = 100.00
    
print('{:.2f}V'.format(voltage))
print('{:.0f}%'.format(percentage))