Electric vehicles and charging

An electric vehicle exposes a set of properties a combustion car simply does not have. If you have only worked on petrol programmes, this is a whole vocabulary you have not met.

It is also the area where getting the presentation wrong causes the most customer complaints, because the numbers involved are estimates that people treat as facts.

Why EV data is different#

The core properties#

State of charge is not a percentage property#

There is no single "percent full" property. You compute it:

val nowWh = properties.getFloatProperty(
    VehiclePropertyIds.EV_BATTERY_LEVEL, GLOBAL,
)
val capacityWh = properties.getFloatProperty(
    VehiclePropertyIds.INFO_EV_BATTERY_CAPACITY, GLOBAL,
)
 
val percent = ((nowWh / capacityWh) * 100f).coerceIn(0f, 100f)

Charging state, and the pair of properties people confuse#

val portOpen = properties.getBooleanProperty(
    VehiclePropertyIds.EV_CHARGE_PORT_OPEN, GLOBAL,
)
val cableIn = properties.getBooleanProperty(
    VehiclePropertyIds.EV_CHARGE_PORT_CONNECTED, GLOBAL,
)

Charge rate carries sign, and the sign is meaningful:

val rateW = properties.getFloatProperty(
    VehiclePropertyIds.EV_BATTERY_INSTANTANEOUS_CHARGE_RATE, GLOBAL,
)
 
when {
    rateW > 0 -> showCharging(rateW)                  // energy going in
    rateW < 0 -> showDischarging(-rateW)              // driving, or V2L
    else      -> showIdle()
}

A negative rate while stationary means the car is powering something — vehicle-to-load, running the cabin, or preconditioning.

Presenting estimates honestly#

This is where the engineering meets the complaint from the top of the page.

val range = properties.getProperty(
    Float::class.java, VehiclePropertyIds.RANGE_REMAINING, GLOBAL,
)
 
when (range?.status) {
    CarPropertyValue.STATUS_AVAILABLE   -> showRange(range.value)
    CarPropertyValue.STATUS_UNAVAILABLE -> showCalculating()   // not a zero
    else                                -> showPercentOnly()
}

Showing 0 km because the property was unavailable is the same silent-failure pattern from the VHAL topics, and here it makes a driver stop at a charger they did not need.

Charging is a long-running background activity#

A car charges for hours, usually unattended, with the head unit suspended.

Writing: limits and switches#

Two properties are writable, and both need care.

properties.setFloatProperty(
    VehiclePropertyIds.EV_CHARGE_PERCENT_LIMIT, GLOBAL, 80f,
)

Many drivers cap at 80% to preserve battery life. The property may only accept specific values — check the config's supported values rather than assuming any percentage works.

properties.setBooleanProperty(
    VehiclePropertyIds.EV_CHARGE_SWITCH, GLOBAL, true,
)

Both need android.car.permission.CONTROL_CAR_ENERGY — signature-level, because they change vehicle behaviour.

Checking what a vehicle actually has#

Combustion vehicles do not have these properties at all, and even among EVs the set differs.

val isElectric = properties.propertyList.any {
    it.propertyId == VehiclePropertyIds.EV_BATTERY_LEVEL
}
 
val canSetLimit = properties.propertyList.any {
    it.propertyId == VehiclePropertyIds.EV_CHARGE_PERCENT_LIMIT
}

adb shell dumpsys car_service --list-properties | grep -i EV_

Next#

Where the vehicle thinks it is, and what happens in a tunnel.