This has been suggested before, with combinations of ultracapacitors and batteries.[1] When a electric vehicle with regenerative braking brakes hard, that can produce more power than the battery can accept for charging. Dumping the energy into ultracapacitors is a good way to store it for a short period.

Laptops? Probably just a gimmick. It won't increase the stored energy.

[1] http://www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_revi... [2] http://www.technologyreview.com/news/417053/a-battery-ultrac...