The simultaneous adoption of battery electric vehicles and switching from privately owned cars to carsharing substantially impacts the release of greenhouse gas emissions, mobility costs and the security of electricity supply. An integrated hourly charging behavior optimization model for charging costs or emissions relying on a large carsharing reservation database is showcased for Switzerland, revealing a strong trade-off between electricity prices and CO₂ emissions. Price-responsive electric charging reduces charging costs by 27% compared to emission-responsive charging, which reduces e-mobility-related CO₂ emissions by 82%. Introducing a dynamic carbon tariff could make emission-responsive charging economically rational, resulting in an average carbon price of EUR 0.3/kg CO₂ -equivalent. Although carsharing hinders battery charging at times of low emissions and requires increased overnight charging, carsharing only leads to minimal differences in operational costs or charging emissions compared to privately owned cars. However, a large-scale shift to battery electric vehicles requires energy system adjustments to meet the additional electricity needs from e-mobility. For complete electrification of private cars by 2050 in Switzerland, an additional curtailment, storage or import capacity of 1.3 TWh for the most critical winter month is required for individual car ownership and an additional 1.0 TWh for shared e-mobility.