My understanding is that the remaining energy from a battery can be approximated using several different methods e.g. measuring the battery voltage. However, I am yet to find a method that is completely accurate.
While some inaccuracy shouldn't generally be an issue when checking your phone's battery percentage, surely a sport like Formula E would need to use the most accurate method to ensure fairness?
For example, in the 2014 Beijing ePrix, 3 drivers were given 57 second penalties for exceeding the maximum energy usage limit of 28kWh. Given a transgression like this can result in such a significant penalty, you would expect that the method for measuring this usage must be highly accurate.
Therefore, I wondered what method they use in Formula E to measure the remaining battery energy?