Next idea!
The Insight's 12v battery sits around 12.5v when the car is off, and ~12.8v when it's on. I assume this has something to do with the battery's internal resistance going up as the voltage increases, or other losses. Anyway, I'm thinking about permanently installing a small battery tender and plugging it in every night, so the DC-DC converter doesn't have to take any energy from the hybrid battery. I imagine with most of my drives, it probably wouldn't even come on before I'm at my destination if I left home with a topped off battery. Anyone have any idea how much charge I'd get overnight out of a small unit like this?
http://www.amazon.com/Battery-Tender-022-0150-DL-WH-Waterproof-Charger/dp/B000CITKCE/
Would it be safe to install permanently under the hood?
EDIT: This one looks to be able to charge faster:
http://www.amazon.com/12V-Battery-Charger-Charging-Waterproof/dp/B00IFE2FKQ/ref=sr_1_21?s=automotive&ie=UTF8&qid=1414952653&sr =1-21&keywords=waterproof+battery+tender