When your solar system produces excess energy to what you are consuming on-site, it will charge your home battery. If the battery is full of charge, the excess will go back to the grid.
When you have energy consumption on-site that is more than what your solar system is producing, the battery will discharge. The battery should never discharge to the grid (unless specified to), it should only discharge to household loads.
Home batteries can only charge and discharge energy at a certain rate (It should not go 0-100% immediately). This is different for each battery.
GivEnergy batteries charge/discharge at a rate of 2.4kWh.
Energizer batteries charge/discharge at a rate of 3.6kWh.
Back-up in the event of a power outage is based on whether you have purchased this additional feature and whether the battery has enough charge at the time.
For example: If you have a power cut in the early morning (6am – 9am), it is most likely the battery won’t have enough charge to sustain power.
Back-up can cover certain circuits, not your entire home. This is again relevant to the discharge capacity of your particular battery.
Batteries should not be used to back up systems that someone’s health relies on. If the battery runs out of charge it will turn off.