ICE Charging Output To Hybrid Battery @ Idle

You can watch it with various apps (or a product like ScanGauge II) using the battery current custom PID, where negative values represent charge going into the battery.

You can see around −15 amps or so, or roughly 3 kW, if you're stationary and not on the go pedal. The engine isn't "idling" then; it's running around the same RPM as idle, but throttled up to do 3 kW of extra work, and you can hear that change in the exhaust note.

The figure is of interest in the thread linked below, because it influences the maximum size of inverter you might usefully attach to the high-voltage system. The engine and MG1 are capable of more than 3 kW, of course, by revving up to higher RPMs, but that just isn't anything the power management control ECU is programmed to do while the car's just sitting there, so in practical terms that 3 kW is about all such a system will have to work with.

Electric power from a hybrid, connecting inverter to the high-voltage system | PriusChat