Our experience is that the Powerwall can be configured to automatically prevent discharging whilst the EV is charging overnight. We do this by putting the Powerwall into Time Based control mode, configuring an energy tariff with a period overnight of cheap-power, and then scheduling the EV to charge only during this period.
This configuration signals to the Powerwall that there is the least value to the owner in discharging during the period when the EV is charging. It relies on the built in control algorithm to choosing not to discharge energy during this period.
Note that the Powerwall won't discharge any energy during this off-peak period, so it won't discharge for your EV charging, but it also won't discharge to meet any home loads.
If you're on an energy tariff that has varying rates at different times of the day, ensure you align your EV charging period with the time that your energy rates are the cheapest.
If you're on a flat rate tariff (the same price for energy any time of the day) with your electricity provider, you can still configure the tariff in the Powerwall (with peak prices during the early evening and off-peak periods overnight) as it still provides the same signal to the battery as to the best time of day to charge and discharge.
