Automation Ev Batt charging -how to trigger a save value when pressing a button?

Would like to automate my ev battery loading mechanism but have no clue on how to do.
I created some helpers around it and what i want to achieve is that autolader switch on automated.
To achieve this I created a button entidy called ‘Autolader Starte Laden’. When I click this button entidy it should save the value of ‘autolader_energy_total’ into ‘autolader_start_charge_battlevel’. how can I make that happen?