MIT researchers have created shock absorbers that generate electricity while performing their function. They estimate 1Kw per shock in a class 8 size shock application. I don't know over what time period. I don't know if they'd provide any real benefit either since the alternator should fully recharge all batteries while driving and the shocks contribute nothing while parked. If they worked in conjunction with a hybrid drive system perhaps they'd be beneficial however the total weight/cost added would likely offset all advantage created. The potential for something like the Prius may be greater. In any event it's an interesting report.