[aurelwu]

it really depends on how much you drive and how co2 intensive the power you use is (which depends not only on your locale but also the time when you charge your car typically). However one thing in the overhead costs which is often ignored is that a used car battery which might not be suited for a car anymore because of 20-30% capacity loss after a few years can be reused in stationary battery systems, so over the full lifetime of the battery the overhead costs in most calculations are overexaggerated.