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come posso misurare la carica di una batteria con xod

If your battery is < 5V, you can connect it to ground and an analog pin, then do an analog_read on that pin. In XOD, analog_read will return a value between 0 and 1; 0 would be 0V, and 1 would be 5V.

If your battery is > 5V, you can use a voltage divider (Voltage divider - Wikipedia) to bring the voltage within range of the Arduino. At its simplest, a voltage divider would be two resistors of the same value. One would connect battery+ to ground, the other would connect battery+ to the analog pin on the Arduino. This would allow you to measure up to 10V since it would halve the voltage.

Alternatively, you could add a voltage sensor to read the voltage of the battery. arduino voltage sensor at DuckDuckGo