I'm a bit confused by this KERS thing. I thought it recovered energy from braking.
Just then Hamilton used a big boost, and used all the energy, down the pit straight but as soon as he crossed the line his KERS was fully charged.
You're only allowed 82bhp for a maximum of 6.6 seconds per lap. You can split it up into 3 to give a general improved lap speed, or a boost to overtake. Them's the rules.