Simple python script using bluetooth to periodically log your phone's battery level from another device.

battery_tracker.py

import asyncio
from bleak import BleakClient, BleakScanner
import time
from datetime import datetime
import sys

print("Bluetooth battery monitoring script launched.")

args = sys.argv
if len(args) < 3:
    print("Usage: python3.9 battery_tracker.py [NAME OF DEVICE] [PATH TO LOGFILE]")
    exit(1)

PHONE_NAME = args[1]
LOGFILE = args[2]

async def main():
    iphone_dev = False;

    ## Discover my device, given its name
    while iphone_dev == False:
        async with BleakScanner() as scanner:
            devices = await scanner.discover(timeout=30.0)
            for d in devices:
                if d.name == PHONE_NAME:
                    iphone_dev = d;
                    break
        print("Scan timed out, trying again.")
        
    print(iphone_dev)
        
    async with BleakClient(iphone_dev.address) as client:
        await client.connect()
        phone_services = client.services
        battery_char = phone_services.get_characteristic(26)
        while True:
            battery_level = int.from_bytes(await client.read_gatt_char(battery_char), byteorder='big')
            with open(LOGFILE, "a") as f:
                f.write(str(datetime.now()) + " " + str(battery_level) + "\n")
                print("Battery logged: " + str(datetime.now()))
            time.sleep(30)
        await client.disconnect()
        
asyncio.run(main())