Charging the EV from the home battery

Sometimes I want to charge my EV from my home battery. Charge HQ currently does not have a feature to do this automatically.

Use cases for this include:

  • My home doesn’t need the whole battery overnight. Eg in summer my home uses less than 50% of my 10 kWh home battery, and the battery is usually full in the evening, so there is at least 5 kWh available for EV charging overnight.
  • The car is in and out multiple times during a sunny day, and the home battery is full during the morning.

A feature which enabled charging from the home battery would adjust the EV charging power so that the total consumption (including the EV) is equal to the discharge power of the battery. This charging would stop when the home battery dropped to a configured state of charge.

Any interest in such a feature?

We realise that most people explicitly do not want to charge their EV from their home battery, because their home battery is mostly or fully utilised to power the home.

This poll on our Facebook group suggests that most people want to reserve at least 80% of their home battery to power the home overnight.

However, analysis of our user’s data shows that there might be a bit more energy left in home batteries (on average) than the poll results might suggest.

I get the concept, but personally I wouldn’t use it, out of concerns to materially contributing to degradation of the home battery.
Firstly, its inefficient as only 90% of the energy comes out - battery-to-battery movements lose 10% of the energy straight away.
Secondly, adding 5kWh to a 60 - 80 kWh car battery barely significant for the car and isn’t likely to be that time-sensitive - I could just charge off the grid or later the next day for just half-hour at 11kW to get the same outcome. But half the home battery capacity at its full rate of discharge is a significant load on the home battery and may contribute to its capacity decline over time.
So personally I’d leave the home battery at 50% overnight, which then means it needs less energy the next day to fill up and has reserve to run the kettle and appliances before the sun rises the next morning. And then the car will fill that 5kWh the next day after the home battery is full, which occurs sooner than it otherwise would have if it started the morning depleted.
Maybe if the car was down to less than 5% SoC - but that would be so rare I’d manually flick CHQ app to ‘charge now’ and fill it up a bit regardless.

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