What I want is the regenerative braking stuff in a standard 4-cylinder, 5-speed, reasonably efficient gas/diesel car.

My miles are 90% highway, so the hybrid route is actually less efficient (adds extra weight). But: if I could charge a modest battery pack from braking, and use it later at home to power/charge all my electronic stuff, that would truly be efficient.

I'm trying to think of ways to add this "after-market" to my fine little Mazda -- but it always ends up looking like a "Mad Max" rod, I'm afraid.