more seriously: what about having a setting for not fully charging the battery (let's say 80-90%), possibly user configurable, so if you don't risk your life if you forget about it?
and finally a question: how does a Prius work? according to this[1] The amount of electrical energy capable of dissipation is limited by either the capacity of the supply system to absorb this energy or on the state of charge of the battery or capacitors. Effective regenerative braking can only occur if the battery or capacitors are not fully charged. For this reason, it is normal to also incorporate dynamic braking to absorb the excess energy.
Searching online I found this[2] that seems to be not that far from my semi joke :) as a user says "instead of taking that energy and putting into the battery, the engine throws it off as heat." But it's also true that a Prius is way more complex and bigger, so it could have more features put in place compared to a small board like this.
[1] http://en.wikipedia.org/wiki/Regenerative_brake [2] http://priuschat.com/threads/fully-charged-hv-battery-no-reg...